US2823118A - Method and apparatus for digesting fibrous material - Google Patents

Method and apparatus for digesting fibrous material Download PDF

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US2823118A
US2823118A US192547A US19254750A US2823118A US 2823118 A US2823118 A US 2823118A US 192547 A US192547 A US 192547A US 19254750 A US19254750 A US 19254750A US 2823118 A US2823118 A US 2823118A
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acid
side relief
digester
accumulator
liquor
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US192547A
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Albert D Merrill
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Chemipulp Process Inc
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Chemipulp Process Inc
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    • 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

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  • the present invention relates to a method and apparatus for digesting fibrous cellulose material and more particularly pertains to improvements in hot acid systems employed in the production of pulp.
  • the cooking liquor contaminated by the organic matter also tends to reduce the yield of pulp and the system requires more sulphur to properly cook a given quantity of cellulosic material.
  • An object of the present invention is to provide an improved method of handling the side relief to prevent the accumulation of organic matter as well as water solubles in the accumulator to thereby preserve the acid strength and to provide for an increased yield of higher quality pulp.
  • Another object of the invention is to provide apparatus for delivering the side relief from the digester into a side relief storage tank as distinguished from the accumulator to thereby avoid contamination of the cooking liquor and at the same time to.
  • a still further object of the invention is to provide apparatus for transferring the heat units of the side relief liquor and gas to the fortified acid entering the system and to deliver the cooled gases to a recoverytower for absorption in the raw acid supply.
  • the single sheet of the annexeddrawing includes a diagrammatic flow chart illustrating a system embodying the. invention and for carrying out theimproved method.
  • the present invention is directed to the removal of the side relieffrom the digester and provides the advantages of recovering the heat and gases contained in the side relief liquor without contaminating the cooking liquor in the high pressure accumulator with organic matter from the digester.
  • the side relief is diverted from the accumulator to thereby prevent the contamination of. the acid and such a method accordingly prevents the degrading of thepulp and a reductionof the yield of pulp when the liquor within the accumulator is employed in subsequent cooking operations.
  • the present invention provides for the recovery of the heat units contained in theside relief liquor and gases and at the same time avoids any loss of free sulphur dioxide.
  • a system for carrying out the present invention may include as elements a digester 1, a high pressure accumulator 2, a low pressure accumulator 3, a side relief storage tank 4, and a degassing tower 5.
  • the apparatus includes as further elements a fortified acid storage tank 6, a recovery tower 7, a raw acid storage tank 8, a weak acid tank 9, and a tail gas absorption tower 10.
  • the digester 1 may be of a conventional construction and a pulp mill embodying the features and principles of the present invention may include a series of digesters one of which is shown in the drawing.
  • the digester is provided with a conventional arrangement for admitting steam and one of such pipe connections is represented at 12 provided with a valve 14.
  • the digester may be provided with a blow-01f elbow 16 and the horizontal arm thereof includes a valve 17.
  • the digester 1 may be filled with wood chips in the usual manner and closed by a man-hole cover 18.
  • a vent line for permitting air to escape from the digester is indicated at 19 and provided with a valve 20. for closing the vent when gas begins to escape; from the digester during the filling operation.
  • the high pressure accumulator 2 is of a conventional construction and may be of any desired shape.
  • a conduit line 21 extends from the lower portion of the high pressure accumulator 2 which is controlled by a hand-operated valve 22.
  • a pump 23 is provided in the line 21 for delivering acid from the high pressure-accumulator into the digester in a manner as well-known in the art. It will be understood that additional digesters (not shown) may be served by the liquor delivered through the line 21.
  • a high pressure relief line 25 extends from the top portion of the digester 1 and this line is controlled by a manually operable valve 26.
  • the high pressure relief line extends to a high pressure eductor 27 and the drop leg 28 thereof is connected to the accumulator through a branch pipe 36 controlled by a valve 29.
  • the high pressure accumulator 2 is provided with a top vent line 31 which is controlled by an automatically operated pressure relief valve 32.
  • the vent line 31 is in open communication with a low pressure relief line 33 which extends from the top of the digester 1 through a manually controlled valve 34.
  • the low pressure relief line 33 extends to a low pressure eductor 36.
  • Apparatus for carrying out the invention may include the low pressure accumulator 3.
  • a drop leg 37 extends from the low pressure eductor 36 and is connected to the low pressure accumulator 3 through a branch pipe 35.
  • a valve 38 may be interposed in the pipe 35.
  • a pipe line 39 extends from the lower portion of the accumulator 3 and a pump 40 moves acid from the low pressure accumulator through the line 39 to the high pressure eductor 27.
  • This fortified acid absorbs the gases in the high pressure line 25 and creates a partial vacuum therein to promote removal of the gases from the digester in a well-known manner.
  • the fortified acid moves from the eductor 27 through the drop leg 28 into the high pressure accumulator.
  • a vent conduit line 41 extends from the top of the low pressure accumulator 3 and terminates in the lower portion of the fortified acid storage tank 6.
  • An automatically operated pressure relief valve 42 is provided in the line 41 for controlling the escape of gas from the low pressure accumulator 3.
  • the digester is provided with a conventional type of strainer assembly (not shown) leading to a side relief line 43.
  • the side relief line 43 is controlled by means of a hand-operated valve 44.
  • the side relief line 43 extends into communication with the side relief storage tank 4 and thus by-passes the high pressure accumulator 2.
  • the present invention avoids delivery of any of the side relief and the organic matter contained therein into the high pressure accumulator and the side relief is delivered into the side relief storage tank 4 through the line 43.
  • a vent line 46 extends from the top of the side relief storage tank 4 into open communication with the low pressure relief line 33 leading into the low pressure eductor 36. Any gases that are removed from the side relief liquor in the side relief storage tank 4 are thereby brought into contact with the fortified acid being delivered into the low pressure accumulator 3.
  • An automatic pressure operated valve 47 is provided in line 46.
  • the side relief liquor within the storage tank 4 is delivered by a pump 48 interposed in a conduit line 49 to a spray nozzle 51 mounted in the upper portion of the degassing tower 5.
  • the degassed liquor present in the tower is lead off through a suction conduit 52 to a pump 53 and this degassed liquor is forced through a pipe 54 into a heat exchanger 56.
  • the heat units remaining in the degassed liquor are transferred to the fortified acid pumped from the tank 6 by a pump 58 and a conduit line 59, which extends through the heat exchanger 56.
  • the degassed liquor from the tower after having given up its heat units is delivered to waste through a pipe 61.
  • a heat exchanger 62 is provided through which the gases vented from the degassing tower 5 are conveyed by a conduit or pipe 63.
  • the fortified acid pumped through the line 59 moves in heat exchange relationship with these gases to further add heat to the liquid from the fortified storage tank 6 on its way to the low pressure cductor 36.
  • a vacuum pump 66 is provided in a pipe line 67 leading from the heat exchanger 62 to further assist in removing all of the free sulphur dioxide contained in the side relief.
  • the gases exhausted by the vacuum pump 66 are delivered through the line 67 into the recovery tower 7 through the branch pipe 68.
  • the sulphur dioxide is absorbed in the recovery tower 7 in a manner as well-known in the art. It will be noted here that substantially all of the free sulphur dioxide contained in the side relief is removed in the degassing tower 5 and such gas is recovered in the reclamation system and the heat thereof is also recovered and added to the fortified acid supply. Under proper operating condittons about twenty-five to forty-three pounds of sulphur are saved per ton of pulp cooked by removing all of the free sulphur dioxide in the degassed tower 5 and by means of the vacuum pump and the associated conduit system.
  • the gases moving through the conduit 63 are cooled by the heat exchanger 62 on ts passage to the vacuum pump 66 and the recovery tower 7.
  • the heat units removed from these gases are transferred to the relatively cool fortified acid passing through the hue 59 on its way to the low pressure eductor 36.
  • the heat umts contained in the side relief liquor are transferred to the fortified acid from the st g t as the fortified acid is pumped to the low pressure cductor 36 through the heat exchanger 56.
  • the hot gases vented from the digester through the lower pressure line 33 are contacted by the fortified acid moving through the low pressure cductor 36 and these gases are absorbed in the fortified acid and the temperature of the acid being delivered into the low pressure accumulator 3 is further increased.
  • the system includes the raw acid storage tank 8 into which raw acid is delivered from the acid make-up means through a pipe 71.
  • a pump '72 delivers the raw acid from the tank 8 into the pipe line '73 which terminates in a spray nozzle 79 mounted in the upper portion of the recovery tower 7.
  • This recovery tower is provided with materials therein for facilitating the absorption of the gases in a manner well-known in the art.
  • the raw acid is sprayed downwardly in the tower 7 from the spray head 79 and flows downwardly through the absorption materials therein against the counter flow of reclaimed gas entering the tower through the line 68.
  • the fortified acid developed in the recovery tower 7 is moved by a pump 76 into a conduit line 77 and delivered into the lower portion of the fortified acid storage tank 6 by means of a depending pipe 78.
  • the tail gas tower 10 is provided with an outlet for waste gases as represented by a pipe 81 which is controlled by a valve 82. Water in metered quantities may be admitted to the tail gas tower it) through a pipe connection 83 controlled by a valve 34.
  • the tail gases within the recovery tower 7 are led through a conduit 86 into the lower portion of the tail gas tower it). These rising tail gases which have not been absorbed by the system acid move upwardly in the tail gas tower 10 against the counter how of a small quantity of water flowing downwardly through the stoneware packed in the tail gas tower It and the resulting weak acid is delivered into the weak acid tank 9 through a conduit fitting 87.
  • the tower 10 is constructed similarly to the tower 7 and the tail gases enter at the base of the tower 10.
  • a relatively small quantity of water is introduced through the conduit 83 into a chamber at the top of the tower 10. This water flowing down through the absorption materials is against the counter flow of the gases.
  • the waste gases, such as carbon dioxide, nitrogen, and oxygen escape at the top of the tower 10 through the vent pipe 81.
  • the recovery of a sulphur dioxide component of the tail gases absorbed in the water moves into the weak acid tank 9.
  • the weak acid may be delivered into the raw acid tank 8 by means of a pump 91 and the conduit 92.
  • a vent line 93 extends from the upper portion of the raw acid storage tank 8 into communication with a branch pipe 94 for leading gas into the lower portion of the recovery tower 7.
  • Another vent line 96 extends from the top ofthe fortified acid storage tank 6. This line leads gas from the tank 6 into the pipe 94 and into the recovery tower 7.
  • the digester 1 is filled with wood chips and the man-hole cover 18 is secured in position closing the digester.
  • the valves 26, 34 and 44 are closed.
  • the valve 20 is opened.
  • the pump 23 is started and the valve 22 is opened so that acid is moved from the high pressure accumulator into the digester 1.
  • the acid liquor is forced into the lower section of the digester and as the level of the entering acid rises, air is progressively displaced and vented olf through the line 19.
  • free sulphur dioxide :or other gas begins to move off the digester and the valve 20 is then closed and the valve 34 is opened to admit such gases to the low pressure line 33.
  • the acid forced from the high pressure accumulator 2 into the digester is at an elevated temperature such evolved gases contain available heat. Such heat units are absorbed by cooler acid moving into the lower pressure accumulator 3 through the cductor 36.
  • the high pressure relief line-25 is placed in communication with the top of the digester by opening the valve 26.
  • the hot acid from the high pressure accumulator 2 is circulated through the line 21 into and through the digester 1 and back to the high pressure accumulator 2 through the high pressure relief line 25 until the temperatures are equalized at the top and bottom of the digester.
  • the cooking cycle is then initiated by admitting steam through the pipe. 12.
  • the relief gases are vented at the start of the cook through the open valve 26 into the high pressure line 25 to the drop leg 28 :of the high pressure eductor 27 where these gases are contacted by the acid delivered into the high pressure eductor 27 from the low pressure accumulator 3.
  • This vented gas which includes steam moves into the low pressure eductor 36 and is absorbed in the fortified acid moving into the drop leg 37.
  • the present invention provides for the delivery of the side relief into the side relief storage tank 4 during the operation of lowering the pres-sure on the digester.
  • the valve 44 is opened the side relief moves through the line 43 into the tank 4 and bypasses the high pressure accumulator 2.
  • Any gas released from the side relief liquor in the side relief storage tank 4 moves through the conduit line 46 into the low pressure eductor 36 for absorption in the acid supply moving into the low pressure accumulator 3.
  • the side relief liquor in the storage tank 4 is delivered by the pump 48' into the conduit line 49 and sprayed downwardly in the degassing tower 5.
  • the side relief liquor in the tower is moved by the pump 53 through the heat exchanger 56 to waste.
  • the heat removed from theside relief liquor moving through the heat exchanger 56 is transferred to the fortified acid moving from the tank 6.
  • the gases released in the degassing tower 5 are led off in the conduit line 63 through the heat exchanger 62 where the heatunits :of the side relief gases are transferred to the fortified acid moving towards the low pressure accumulator 3.
  • the removal of the free sulphur dioxide is further facilitated by the vacuum pump 66 and these cool gases move into the lower portion .of the recovery tower 7 through the pipes 67 and 68.
  • the present invention provides for the recovery of the heat units in the side relief liquor and the heat units of side relief gases. It will be further noted that all the free sulphur dioxide released from the side relief liquor is recovered and reclaimed.
  • a digester In apparatus for digesting cellulosic material, a digester, an accumulator, means for moving cooking liquor from the accumulator into the digester, a side relief storage tank, a conduit line extending from the digester from a point below the top and above the bottom thereof into communication with the side relief storage tank, a closed degassing tower, a spray head in a top portion of said degassing tower, means for pumping liquid and the contained gases from the side relief storage tank to said spray head, a supply of acid, means for moving acid from said supply to the accumulator, means for transferring heat units from the gas released in the degassing tower to the acid moving towards the accumulator, means for absorbing substantially all of the cooled gases inthe acid supply, means for transferring heat units of the side relief liquid to the acid supply, and means for delivering the cooled and degassed side relief liquor to waste.
  • a digester In apparatus for digesting fibrous material, a digester, an accumulator, means for moving cooking liquor from the accumulator into the digester, a side relief storage tank, a conduit line extending from the digester at a point below the top and above the bottom thereof into communication with the side relief storage tank, a closed degassing tower, a spray head in the top portion of said degassing tower, means for pumping liquid and contained gases from the side relief storage tank to said spray head, a supply of acid, means including a conduit line for moving acid from said supply to the accumulator, heat transferring means in said conduit line, means including a vacuum pump moving gas released in the degassing tower through said heat exchange means to transfer heat to the acid moving towards the accumulator, means for absorbing the cooled gas in the acid supply, means for transferring heat units of the side relief liquid to the acid moving to the accumulator, and means for delivering the side relief liquor to waste.
  • a digester for digesting fibrous material, said digester having a side relief opening at a point below the top and above the bottom thereof, a high pressure accumulator, conduit means including a pump for moving liquor from the high pressure accumulator into the digester, means for returning liquor from the digester to the high pressure accumulator, a low pressure accumulator, a supply of acid, means including a low pressure eductor for moving acid from said supply to said low pressure accumulator, a low pressure conduit line leading from the top of the digester to the low pressure eductor, a side relief storage tank, a pipe line extending from said side relief opening into communication with the side relief storage tank, a degassing tower including a spray head in an upper portion thereof, means for pumping the side relief liquid and the contained gases from the side relief storage tank under pressure to said spray head, conduit means leading from the top of said storage tank into communication with said low pressure conduit line, a heat exchange device associated with the means for moving acid to the low pressure accumulator
  • a digester in a hot acid system for digesting fibrous material, said digester having a side relief opening at a point below the top and above the bottom thereof, a high pressure accumulator, means for moving liquor from the high pressure accumulator into the digester, means for 7 returningjthe liquor from the digester to the high pressure accumulator, a low pressure accumulator, a supply of acid, means including a low pressure eductor for moving acid from saidsupply to said low pressure accumulator, a low pressure conduit line leading from the top of the digester to the low pressure eductor, a side relief storage tank, a conduit line extending from the side relief opening into communication with the side relief storage tank, a closed degassing tower including a spray head in an upper portion thereof, means for pumping liquor and the contained gases from the side relief storage tank to said spray head, a conduit line leading from the top of said storage tank into communication with said low pressure line, heat transfer means in heat exchange relation with the means for moving acid to the low pressure accumulator, means including
  • a method of digesting fibrous material which comprises, accumulating a supply of digestion liquor in an accumulator, charging a digester with fibrous material,
  • a method of digesting fibrous material which comprises, storing digesting liquor in an accumulator, charging a digester with fibrous material, moving liquor from the accumulator into the digester, cooking the fibrous material in the digester, venting side relief having a major portion in the liquid state from the digester at a point below the top and above the bottom before termination of the cooking step, guiding the side relief into a storage tank separate from the accumulator so that organic matter contained in the side relief enters the storage tank, moving raw acid from a supply source to the accumulator tank, removing gas from the side relief, transferring heat units from the gas to the raw acid moving to said accumulator, absorbing said released gas in said acid supply, and
  • a method of digesting fibrous material which comprises, storing cooking liquor in an accumulator, charging the digester with fibrous material, moving liquor from the accumulator into the digester, cooking the fibrous material within the digester, venting side relief having a major portion in a liquid state from the digester at a point below the top and above the bottom thereof before termination of the cooking step, guiding the side relief liquor into a storage tank without delivering said side relief into the accumulator, spraying the liquid side relief under pressure into a closed degassing tower to remove gases from the side relief liquor, moving acid from a supply source into the accumulator, transferring heat units from said released gases to the acid moving to the accumulator, absorbing the cooled free sulphur dioxide component ofsaid gases in the supply of acid, discharging other components of the gases to waste, transferring heat units of the side relief liquor to the acid moving to the accumulator, and discharging the cooled degassed side relief liquor to waste.
  • a method of digesting fibrous material which comprises, storing sulphite liquor in an accumulator, charging the digester with fibrous material, moving liquor from the accumulator into the digester, cooking the fibrous material in the digester, venting side relief having a major portion in a liquid state from the digester at a point below the top and above the bottom thereof before termination of the cooking step, guiding the side relief liquor into a closed storage tank without delivering said side relief into the accumulator, moving acid from a supply source into the accumulator, guiding sulphur dioxide released in said tank into a position for absorption in said acid moving to the accumulator, spraying the liquid side relief under pressure into a closed degassing tower to remove gases from the side relief liquor, transferring heat units from said released gases to the acid moving to the accumulator, absorbing the cooled free sulphur dioxide component of said gases in the supply of acid, transferring heat units of the side relief liquor to the acid moving to the accumulator, and discharging the cooled degassed side relief

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Description

Feb. 11, 1958 A. D. MERRILL METHOD AND- APPARATUS FOR DIGESTING FIBROUS MATERIAL Filed Oct. 27, 1950 kmwkgX M E INVENTOR [LEE/PTLVIERR/LL,
BY 61. w m
ATTORNEY United States Patent METHOD AND APPARATUS FOR DIGESTING FIBROUS MATERIAL Albert l). Merrill, WatertoWn, N. Y., assignor to Chemipnlp Process, Inc., Watertown, N. Y.
Application October 27, 1950, Serial No. 192,547
8 Claims. (Cl. 92--11) The present invention relates to a method and apparatus for digesting fibrous cellulose material and more particularly pertains to improvements in hot acid systems employed in the production of pulp.
it has been the practice in the past in the normal operation of a sulphite mill to release cooking liquor from the digester in order to lower the pressure therein. The side relief has in the past been delivered through the high pressure relief line into the high pressure accumulator. The side relief liquor contains a substantial amount of organic matter which contaminates the cooking liquor in the high pressure accumulator. Thus when the acid in the high pressure accumulator is subsequently used to fill the digester or other digesters, these organic elements were carried into the next cook. The cooking acid containing material amounts of organic matter provides impure acid and is detrimental to subsequent cooking. Such contaminated cooking liquor tends to reduce the quality factor of the pulp such as the tearing strength, the folding endurance and the bursting strength. in addition, the cooking liquor contaminated by the organic matter also tends to reduce the yield of pulp and the system requires more sulphur to properly cook a given quantity of cellulosic material. In the past it has been necessary to periodically empty and flush out the high pressure accumulator and such steps have been required on the average of: several times during each year of normal operation.
An object of the present invention, therefore, is to provide an improved method of handling the side relief to prevent the accumulation of organic matter as well as water solubles in the accumulator to thereby preserve the acid strength and to provide for an increased yield of higher quality pulp.
Another object of the invention is to provide apparatus for delivering the side relief from the digester into a side relief storage tank as distinguished from the accumulator to thereby avoid contamination of the cooking liquor and at the same time to. employ the side relief liquor as a continuous spray in a degassing tower under pressure so as to remove and reclaim substantially all of the free sulphur dioxide contained in the side relief and to thereby provide a saving in the sulphur required for each unit of pulp cooked.
A still further object of the invention is to provide apparatus for transferring the heat units of the side relief liquor and gas to the fortified acid entering the system and to deliver the cooled gases to a recoverytower for absorption in the raw acid supply.
Other and equally important; objects of the; invention will be apparent and appreciated by those skilledin the art as the present disclosure proceeds and upon consideration of the acompanying drawing and the following detailed description wherein an exemplary embodiment of apparatus exhibiting. the invention and which may be employed in carrying out the process is disclosed.
The single sheet of the annexeddrawing includes a diagrammatic flow chart illustrating a system embodying the. invention and for carrying out theimproved method.
The present invention is directed to the removal of the side relieffrom the digester and provides the advantages of recovering the heat and gases contained in the side relief liquor without contaminating the cooking liquor in the high pressure accumulator with organic matter from the digester. The side relief is diverted from the accumulator to thereby prevent the contamination of. the acid and such a method accordingly prevents the degrading of thepulp and a reductionof the yield of pulp when the liquor within the accumulator is employed in subsequent cooking operations. In addition the present invention provides for the recovery of the heat units contained in theside relief liquor and gases and at the same time avoids any loss of free sulphur dioxide. The principles of the invention as hereinabove expressed may be readily appreciated from a consideration of a specific method in which they are embodied and apparatus in which they are adapted to be effectuated as shown in the drawing. A system for carrying out the present invention may include as elements a digester 1, a high pressure accumulator 2, a low pressure accumulator 3, a side relief storage tank 4, and a degassing tower 5. The apparatus includes as further elements a fortified acid storage tank 6, a recovery tower 7, a raw acid storage tank 8, a weak acid tank 9, and a tail gas absorption tower 10.
The digester 1 may be of a conventional construction and a pulp mill embodying the features and principles of the present invention may include a series of digesters one of which is shown in the drawing. The digester is provided with a conventional arrangement for admitting steam and one of such pipe connections is represented at 12 provided with a valve 14. The digester may be provided with a blow-01f elbow 16 and the horizontal arm thereof includes a valve 17. The digester 1 may be filled with wood chips in the usual manner and closed by a man-hole cover 18. A vent line for permitting air to escape from the digester is indicated at 19 and provided with a valve 20. for closing the vent when gas begins to escape; from the digester during the filling operation.
The high pressure accumulator 2 is of a conventional construction and may be of any desired shape. A conduit line 21 extends from the lower portion of the high pressure accumulator 2 which is controlled by a hand-operated valve 22. A pump 23 is provided in the line 21 for delivering acid from the high pressure-accumulator into the digester in a manner as well-known in the art. It will be understood that additional digesters (not shown) may be served by the liquor delivered through the line 21.
A high pressure relief line 25 extends from the top portion of the digester 1 and this line is controlled by a manually operable valve 26. The high pressure relief line extends to a high pressure eductor 27 and the drop leg 28 thereof is connected to the accumulator through a branch pipe 36 controlled by a valve 29. The high pressure accumulator 2 is provided with a top vent line 31 which is controlled by an automatically operated pressure relief valve 32. The vent line 31 is in open communication with a low pressure relief line 33 which extends from the top of the digester 1 through a manually controlled valve 34. The low pressure relief line 33 extends to a low pressure eductor 36.
Apparatus for carrying out the invention may include the low pressure accumulator 3. A drop leg 37 extends from the low pressure eductor 36 and is connected to the low pressure accumulator 3 through a branch pipe 35. A valve 38 may be interposed in the pipe 35. A pipe line 39 extends from the lower portion of the accumulator 3 and a pump 40 moves acid from the low pressure accumulator through the line 39 to the high pressure eductor 27. This fortified acid absorbs the gases in the high pressure line 25 and creates a partial vacuum therein to promote removal of the gases from the digester in a well-known manner. The fortified acid moves from the eductor 27 through the drop leg 28 into the high pressure accumulator. A vent conduit line 41 extends from the top of the low pressure accumulator 3 and terminates in the lower portion of the fortified acid storage tank 6. An automatically operated pressure relief valve 42 is provided in the line 41 for controlling the escape of gas from the low pressure accumulator 3.
The digester is provided with a conventional type of strainer assembly (not shown) leading to a side relief line 43. The side relief line 43 is controlled by means of a hand-operated valve 44. In apparatus for carrying out the present invention the side relief line 43 extends into communication with the side relief storage tank 4 and thus by-passes the high pressure accumulator 2. The present invention avoids delivery of any of the side relief and the organic matter contained therein into the high pressure accumulator and the side relief is delivered into the side relief storage tank 4 through the line 43.
A vent line 46 extends from the top of the side relief storage tank 4 into open communication with the low pressure relief line 33 leading into the low pressure eductor 36. Any gases that are removed from the side relief liquor in the side relief storage tank 4 are thereby brought into contact with the fortified acid being delivered into the low pressure accumulator 3. An automatic pressure operated valve 47 is provided in line 46.
The side relief liquor within the storage tank 4 is delivered by a pump 48 interposed in a conduit line 49 to a spray nozzle 51 mounted in the upper portion of the degassing tower 5. The degassed liquor present in the tower is lead off through a suction conduit 52 to a pump 53 and this degassed liquor is forced through a pipe 54 into a heat exchanger 56. Thus the heat units remaining in the degassed liquor are transferred to the fortified acid pumped from the tank 6 by a pump 58 and a conduit line 59, which extends through the heat exchanger 56. The degassed liquor from the tower after having given up its heat units is delivered to waste through a pipe 61.
A heat exchanger 62 is provided through which the gases vented from the degassing tower 5 are conveyed by a conduit or pipe 63. The fortified acid pumped through the line 59 moves in heat exchange relationship with these gases to further add heat to the liquid from the fortified storage tank 6 on its way to the low pressure cductor 36. A vacuum pump 66 is provided in a pipe line 67 leading from the heat exchanger 62 to further assist in removing all of the free sulphur dioxide contained in the side relief. The gases exhausted by the vacuum pump 66 are delivered through the line 67 into the recovery tower 7 through the branch pipe 68.
The sulphur dioxide is absorbed in the recovery tower 7 in a manner as well-known in the art. It will be noted here that substantially all of the free sulphur dioxide contained in the side relief is removed in the degassing tower 5 and such gas is recovered in the reclamation system and the heat thereof is also recovered and added to the fortified acid supply. Under proper operating condittons about twenty-five to forty-three pounds of sulphur are saved per ton of pulp cooked by removing all of the free sulphur dioxide in the degassed tower 5 and by means of the vacuum pump and the associated conduit system.
It will be further observed that the gases moving through the conduit 63 are cooled by the heat exchanger 62 on ts passage to the vacuum pump 66 and the recovery tower 7. Thus the gases are in a condition so as to be more readily absorbed in the recovery tower 7. The heat units removed from these gases are transferred to the relatively cool fortified acid passing through the hue 59 on its way to the low pressure eductor 36. The heat umts contained in the side relief liquor are transferred to the fortified acid from the st g t as the fortified acid is pumped to the low pressure cductor 36 through the heat exchanger 56. The hot gases vented from the digester through the lower pressure line 33 are contacted by the fortified acid moving through the low pressure cductor 36 and these gases are absorbed in the fortified acid and the temperature of the acid being delivered into the low pressure accumulator 3 is further increased.
The system includes the raw acid storage tank 8 into which raw acid is delivered from the acid make-up means through a pipe 71. A pump '72 delivers the raw acid from the tank 8 into the pipe line '73 which terminates in a spray nozzle 79 mounted in the upper portion of the recovery tower 7. This recovery tower is provided with materials therein for facilitating the absorption of the gases in a manner well-known in the art. The raw acid is sprayed downwardly in the tower 7 from the spray head 79 and flows downwardly through the absorption materials therein against the counter flow of reclaimed gas entering the tower through the line 68. The fortified acid developed in the recovery tower 7 is moved by a pump 76 into a conduit line 77 and delivered into the lower portion of the fortified acid storage tank 6 by means of a depending pipe 78.
The tail gas tower 10 is provided with an outlet for waste gases as represented by a pipe 81 which is controlled by a valve 82. Water in metered quantities may be admitted to the tail gas tower it) through a pipe connection 83 controlled by a valve 34. The tail gases within the recovery tower 7 are led through a conduit 86 into the lower portion of the tail gas tower it). These rising tail gases which have not been absorbed by the system acid move upwardly in the tail gas tower 10 against the counter how of a small quantity of water flowing downwardly through the stoneware packed in the tail gas tower It and the resulting weak acid is delivered into the weak acid tank 9 through a conduit fitting 87. The tower 10 is constructed similarly to the tower 7 and the tail gases enter at the base of the tower 10. A relatively small quantity of water is introduced through the conduit 83 into a chamber at the top of the tower 10. This water flowing down through the absorption materials is against the counter flow of the gases. The waste gases, such as carbon dioxide, nitrogen, and oxygen escape at the top of the tower 10 through the vent pipe 81. The recovery of a sulphur dioxide component of the tail gases absorbed in the water moves into the weak acid tank 9. The weak acid may be delivered into the raw acid tank 8 by means of a pump 91 and the conduit 92.
A vent line 93 extends from the upper portion of the raw acid storage tank 8 into communication with a branch pipe 94 for leading gas into the lower portion of the recovery tower 7. Another vent line 96 extends from the top ofthe fortified acid storage tank 6. This line leads gas from the tank 6 into the pipe 94 and into the recovery tower 7. g
In operation the digester 1 is filled with wood chips and the man-hole cover 18 is secured in position closing the digester. The valves 26, 34 and 44 are closed. The valve 20 is opened. The pump 23 is started and the valve 22 is opened so that acid is moved from the high pressure accumulator into the digester 1. The acid liquor is forced into the lower section of the digester and as the level of the entering acid rises, air is progressively displaced and vented olf through the line 19. As the level of the liquor rises free sulphur dioxide :or other gas begins to move off the digester and the valve 20 is then closed and the valve 34 is opened to admit such gases to the low pressure line 33. Since the acid forced from the high pressure accumulator 2 into the digester is at an elevated temperature such evolved gases contain available heat. Such heat units are absorbed by cooler acid moving into the lower pressure accumulator 3 through the cductor 36.
As soon as the digester 1 has been filled with acid from the, accumulator 2, the high pressure relief line-25 is placed in communication with the top of the digester by opening the valve 26. The hot acid from the high pressure accumulator 2 is circulated through the line 21 into and through the digester 1 and back to the high pressure accumulator 2 through the high pressure relief line 25 until the temperatures are equalized at the top and bottom of the digester. The cooking cycle is then initiated by admitting steam through the pipe. 12. At the initiation of' the cooking operation the relief gases are vented at the start of the cook through the open valve 26 into the high pressure line 25 to the drop leg 28 :of the high pressure eductor 27 where these gases are contacted by the acid delivered into the high pressure eductor 27 from the low pressure accumulator 3. This absorbs the gas and reduces the pressure in the line 25 to facilitate the removal of gases from the digester. An hour or more before the termination of the cooking period the valve 26 is closed and the valve 34 is opened and the pressure on the digester 1 is pulled down as low as possible and to a range .of about twenty or twenty-five pounds by the use of the low pressure relief line 33 and the low pressure eductor 36. This vented gas which includes steam moves into the low pressure eductor 36 and is absorbed in the fortified acid moving into the drop leg 37.
At one interval during the cook period and normally about three or four hours before the end of the cook, it has-been preferred to open the side relief valve 44 and this side relief was previously permitted to enter the high pressure relief line so that the side relief was moved into the high pressure. accumulator 2. Such an operation carried organic matter into the cooking liquor within the high pressure accumulator 2. This contaminated liquor in being used to fill the next digester produced inferior pulp and also reduced the yield.
As distinguished from the prior practice the present invention provides for the delivery of the side relief into the side relief storage tank 4 during the operation of lowering the pres-sure on the digester. Thus when the valve 44 is opened the side relief moves through the line 43 into the tank 4 and bypasses the high pressure accumulator 2. Any gas released from the side relief liquor in the side relief storage tank 4 moves through the conduit line 46 into the low pressure eductor 36 for absorption in the acid supply moving into the low pressure accumulator 3.
The side relief liquor in the storage tank 4 is delivered by the pump 48' into the conduit line 49 and sprayed downwardly in the degassing tower 5. The side relief liquor in the tower is moved by the pump 53 through the heat exchanger 56 to waste. The heat removed from theside relief liquor moving through the heat exchanger 56 is transferred to the fortified acid moving from the tank 6.
The gases released in the degassing tower 5 are led off in the conduit line 63 through the heat exchanger 62 where the heatunits :of the side relief gases are transferred to the fortified acid moving towards the low pressure accumulator 3. The removal of the free sulphur dioxide is further facilitated by the vacuum pump 66 and these cool gases move into the lower portion .of the recovery tower 7 through the pipes 67 and 68.
Thus it will be appreciated that the organic matter withdrawn from the digester through the side relief line does not contaminate the cooking liquor. In addition, the present invention provides for the recovery of the heat units in the side relief liquor and the heat units of side relief gases. It will be further noted that all the free sulphur dioxide released from the side relief liquor is recovered and reclaimed.
While the invention has been described with reference to a particular hot acid system and with regard to one series of method steps, it will be appreciated that changes may be made in the apparatus as well as the process of 6 producingpulp. Such changes .and others may be made without departing from the spirit and scope of the invention as set forth in the appended claims.
What I claim and desire to secure by Letters Patent is:
I. In apparatus for digesting cellulosic material, a digester, an accumulator, means for moving cooking liquor from the accumulator into the digester, a side relief storage tank, a conduit line extending from the digester from a point below the top and above the bottom thereof into communication with the side relief storage tank, a closed degassing tower, a spray head in a top portion of said degassing tower, means for pumping liquid and the contained gases from the side relief storage tank to said spray head, a supply of acid, means for moving acid from said supply to the accumulator, means for transferring heat units from the gas released in the degassing tower to the acid moving towards the accumulator, means for absorbing substantially all of the cooled gases inthe acid supply, means for transferring heat units of the side relief liquid to the acid supply, and means for delivering the cooled and degassed side relief liquor to waste.
2. In apparatus for digesting fibrous material, a digester, an accumulator, means for moving cooking liquor from the accumulator into the digester, a side relief storage tank, a conduit line extending from the digester at a point below the top and above the bottom thereof into communication with the side relief storage tank, a closed degassing tower, a spray head in the top portion of said degassing tower, means for pumping liquid and contained gases from the side relief storage tank to said spray head, a supply of acid, means including a conduit line for moving acid from said supply to the accumulator, heat transferring means in said conduit line, means including a vacuum pump moving gas released in the degassing tower through said heat exchange means to transfer heat to the acid moving towards the accumulator, means for absorbing the cooled gas in the acid supply, means for transferring heat units of the side relief liquid to the acid moving to the accumulator, and means for delivering the side relief liquor to waste.
3. In a hot acid system for digesting fibrous material, a digester, said digester having a side relief opening at a point below the top and above the bottom thereof, a high pressure accumulator, conduit means including a pump for moving liquor from the high pressure accumulator into the digester, means for returning liquor from the digester to the high pressure accumulator, a low pressure accumulator, a supply of acid, means including a low pressure eductor for moving acid from said supply to said low pressure accumulator, a low pressure conduit line leading from the top of the digester to the low pressure eductor, a side relief storage tank, a pipe line extending from said side relief opening into communication with the side relief storage tank, a degassing tower including a spray head in an upper portion thereof, means for pumping the side relief liquid and the contained gases from the side relief storage tank under pressure to said spray head, conduit means leading from the top of said storage tank into communication with said low pressure conduit line, a heat exchange device associated with the means for moving acid to the low pressure accumulator, means including a vacuum pump for exhausting gas from said degassing tower and moving it through said heat exchange device, a reclaiming tower associated with the acid supply, means guiding the cooled gas to said reclaiming tower for absorption in the acid supply, means for guiding the side relief liquor from the degassing tower to waste, and means for transferring heat units of the side relief liquor to the acid as it moves towards the low pressure eductor.
4. In a hot acid system for digesting fibrous material, a digester, said digester having a side relief opening at a point below the top and above the bottom thereof, a high pressure accumulator, means for moving liquor from the high pressure accumulator into the digester, means for 7 returningjthe liquor from the digester to the high pressure accumulator, a low pressure accumulator, a supply of acid, means including a low pressure eductor for moving acid from saidsupply to said low pressure accumulator, a low pressure conduit line leading from the top of the digester to the low pressure eductor, a side relief storage tank, a conduit line extending from the side relief opening into communication with the side relief storage tank, a closed degassing tower including a spray head in an upper portion thereof, means for pumping liquor and the contained gases from the side relief storage tank to said spray head, a conduit line leading from the top of said storage tank into communication with said low pressure line, heat transfer means in heat exchange relation with the means for moving acid to the low pressure accumulator, means including a vacuum pump for exhausting gas from the degassing tower and moving it through said heat transfer means, means for absorbing the cooled gas in said acid, means for guiding the side relief liquor from the degassing tower to waste, and means for transferring heat units of the side relief liquor to the acid moving towards the low pressure eductor.
5. A method of digesting fibrous material which comprises, accumulating a supply of digestion liquor in an accumulator, charging a digester with fibrous material,
moving liquor from the accumulator into the digester, cooking the fibrous material in the digester, venting side relief having a major portion in a liquid phase from the digester at a point below the top and above the bottom before completion of the cooking step, guiding the side relief into a storage tank so that organic matter contained in the side relief enters the storage tank and does not move into the accumulator, moving raw acid from a supply source to the accumulator, transferring heat units from the side relief liquor to the raw acid moving to the accumulator, removing gas from the side relief, transferring heat units from the gas to the raw acid moving to said accumulator, absorbing said released gas in said acid supply, and discharging the cooled side relief liquor to waste.
6. A method of digesting fibrous material which comprises, storing digesting liquor in an accumulator, charging a digester with fibrous material, moving liquor from the accumulator into the digester, cooking the fibrous material in the digester, venting side relief having a major portion in the liquid state from the digester at a point below the top and above the bottom before termination of the cooking step, guiding the side relief into a storage tank separate from the accumulator so that organic matter contained in the side relief enters the storage tank, moving raw acid from a supply source to the accumulator tank, removing gas from the side relief, transferring heat units from the gas to the raw acid moving to said accumulator, absorbing said released gas in said acid supply, and
discharging the side relief liquor to waste.
7. A method of digesting fibrous material which comprises, storing cooking liquor in an accumulator, charging the digester with fibrous material, moving liquor from the accumulator into the digester, cooking the fibrous material within the digester, venting side relief having a major portion in a liquid state from the digester at a point below the top and above the bottom thereof before termination of the cooking step, guiding the side relief liquor into a storage tank without delivering said side relief into the accumulator, spraying the liquid side relief under pressure into a closed degassing tower to remove gases from the side relief liquor, moving acid from a supply source into the accumulator, transferring heat units from said released gases to the acid moving to the accumulator, absorbing the cooled free sulphur dioxide component ofsaid gases in the supply of acid, discharging other components of the gases to waste, transferring heat units of the side relief liquor to the acid moving to the accumulator, and discharging the cooled degassed side relief liquor to waste.
8. A method of digesting fibrous material which comprises, storing sulphite liquor in an accumulator, charging the digester with fibrous material, moving liquor from the accumulator into the digester, cooking the fibrous material in the digester, venting side relief having a major portion in a liquid state from the digester at a point below the top and above the bottom thereof before termination of the cooking step, guiding the side relief liquor into a closed storage tank without delivering said side relief into the accumulator, moving acid from a supply source into the accumulator, guiding sulphur dioxide released in said tank into a position for absorption in said acid moving to the accumulator, spraying the liquid side relief under pressure into a closed degassing tower to remove gases from the side relief liquor, transferring heat units from said released gases to the acid moving to the accumulator, absorbing the cooled free sulphur dioxide component of said gases in the supply of acid, transferring heat units of the side relief liquor to the acid moving to the accumulator, and discharging the cooled degassed side relief liquor to waste.
References Cited in the file of this patent UNITED STATES PATENTS 1,263,486 Thornc Apr. 23, 1918 1,599,488 Richter Sept. 14, 1926 1,723,800 Michael et al. Aug. 6, 1929 1,804,967 Wolf et al May 12, 1931 1,908,615 Oman May 9, 1933 1,955,057 Dunbar Apr. 17, 1934 2,029,360 Dean Feb. 4, 1936 2,152,267 Merrill Mar. 28, 1939 2,165,644 Merrill et al July 11, 1939 2,205,374 Dunbar June 18, 1940 2,221,066 Kahle Nov. 12, 1940 2,225,771 Dunbar Dec. 24, 1940 2,494,098 Lockman Jan. 10, 1950 FOREIGN PATENTS 43,007 1 Norway July 26, 1926

Claims (1)

1. IN APPARATUS FOR DIGESTING CELLULOSIC MATERIAL, A DIGESTER, AN ACCUMULATOR, MEANS FOR MOVING COOKING LIQUOR FROM THE ACCUMULATOR INTO THE DIGESTER, A SIDE RELIEF STORAGE TANK, A CONDUIT LINE EXTENDING FROM THE DIGESTER FROM A POINT BELOW THE TOP AND ABOVE THE BOTTOM THEREOF INTO COMMUNICATION WITH THE SIDE RELIEF STORAGE TANK, A CLOSED DEGASSING TOWER, A SPRAY HEAD IN A TOP PORTION OF SAID DEGASSING TOWER, MEANS FOR PUMPING LIQUID AND THE CONTAINED GASES FROM THE SIDE RELIEF STORAGE TANK TO SAID SPRAY HEAD, A SUPPLY OF ACID, MEANS FOR MOVING ACID FROM SAID SUPPLY TO THE ACCUMULATR, MEANS FOR TRANSFERRING HEAT UNITS FROM THE GAS RELEASED IN THE DEGASSING TOWER TO THE ACID MOVING TOWARDS THE ACCUMULATOR, MEANS FOR ABSORBING SUBSTANTIALLY ALL OF THE COOLED GASES IN THE ACID SUPPLY, MEANS FOR TRANSFERRING HEAT UNITS OF THE SIDE RELIEF LIQUID TO THE ACID SUPPLY, AND MEANS FOR DELIVERING THE COOLED AND DEGASSED SIDE RELEF LIQUOR TO WASTE.
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US11458414B2 (en) 2013-10-13 2022-10-04 Synergy Burcell Technologies, Llc Methods and apparatus utilizing vacuum for breaking organic cell walls

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US20080014112A1 (en) * 2006-07-17 2008-01-17 Olaf Nathan Lee Process and apparatus for transforming waste materials into fuel
US7497392B2 (en) 2006-07-17 2009-03-03 Alliance Technology Group, Inc. Process and apparatus for transforming waste materials into fuel
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US8034132B2 (en) 2006-07-17 2011-10-11 Visiam, Llc Process and apparatus for transforming waste materials into fuel
US11458414B2 (en) 2013-10-13 2022-10-04 Synergy Burcell Technologies, Llc Methods and apparatus utilizing vacuum for breaking organic cell walls

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