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
  • D21C7/00—Digesters
  • D21C7/06—Feeding devices

Definitions

• Feeding system in connection with the continuous cooking of cellulose containing material
• the present invention relates to a feeding system for feeding comminuted cellulose containing material and liquid to a continuously operating treatment vessel, preferably a preimpregnation vessel or a digester which may be of steam/liquor phase type or of a hydraulically filled type.
• the feeding system comprises a chute, operating at a first pressure level, with a liquid level and a level of material, a high pressure feeder which, by means of rotating pockets, sluices the material, together with all or a part of said liquid, to a second pressure level, which is higher than said first pressure level, for further conveyance to said treatment vessel, which high pressure feeder also receives a return liquid flow, from said treatment vessel, at said second pressure level and recirculates a recirculation flow to said chute or to said high pressure feeder.
• a conventional feeding system comprises a chip bin, a chip meter, a low-pressure feeder, a steaming vessel, a chip chute and a high-pressure feeder.
• the function of the high-pressure feeder is to sluice the cellulose material, including some liquid, to a continuous digester or to a preimpregnation vessel, which operates at a relatively high pressure.
• Between the high pressure feeder and the impregnation vessel or digester there is conventionally atop circulation, which comprises a feed line for a mixture of chips and impregnation liquid, and a return liquid line for separated impregnation liquid.
• a top separator is arranged in the top of the impregnation vessel or the digester for feeding of the chips into the impregnation vessel or digester at the same time as a part of the impregnation liquid is separated off and is pumped with a pump through the return liquid line, back to the high pressure feeder.
• the high pressure feeder is equipped with a rotor with pockets, whereby one pocket always is in low pressure position, to be in open connection with the chute and one pocket always, at the same time, is in high pressure position, to be in open connection with the impregnation vessel or digester via the feed line.
• the circulation loop is also, as will be further described in connection with the figure description below, equipped with a sand trap and a tubular screen, referred to as an in-line drainer. Further, a level tank is, via a line from the in-line drainer, connected to the return liquid line of the top circulation.
• the building volume needs to be relatively large in order to accommodate the high pressure feeder which must be placed at a relatively high level due to the necessary suction pipe for the pump on the low pressure liquid side of the high pressure feeder. Also the building volume needs to be large enough to accommodate said sand trap, in-line drainer and level tank and this equipment also leads to investment and operating costs.
• a well functioning feeding system can be provided, which feeding system operates substantially without a screening device in the outlet of the high pressure feeder to the circulation loop and also without an in-line drainer and a level tank.
• the system according to the invention further enables the pockets of the high pressure feeder to be filled to a theoretical maximum degree, that is to the same degree as the filling degree in the chute.
• the background of the discovery that has led to the invention is that the machines in modern pulp mills with high production are much larger than they were at the time when the conventional feeding system was developed.
• the pump in the circulation loop, for recirculating liquid to the chute on the low pressure side of the high pressure feeder is much larger today and is hence capable of handling a certain amount of chips in the liquid flow to be pumped, since the size of the chips is not much different from what it always has been.
• the screening device that conventionally stopped chips from entering this circulation, can be excluded, which leads to several important advantages.
• the treatment vessel when a pocket of the high pressure feeder moves towards the low pressure position it is full with liquid from the return liquid flow from the digester or preimpregnation vessel, hereinafter called the treatment vessel.
• the pocket When the pocket reaches the low-pressure position, the liquid is displaced from above with the mixture of chips and liquid that is present in the chute, whereby the same filling degree as in the chute can be achieved.
• the filling degree in the chute is normally about 80-85 vol.-% since some excess liquid is demanded for the chip column to be able to move down into the high- pressure feeder.
• the building height of the high-pressure feeder can be lowered. This is a consequence of the fact that essentially no suction pipe is needed for the pump in the recirculation flow of the circulation loop, since there is no pressure drop across a screening device.
• the conventional level tank and its in-line drainer can be excluded from the system, which results in decreased investment and operating costs as well as in a smaller building volume.
• the reason for the possibility to exclude the level tank and the in-line drainer is that in the system according to the invention, there is always liquid communication between the pumps on the liquid side of the high pressure feeder, and the chute. This means that a chute liquid level control valve can be placed in connection with one of these pumps, for regulation of the liquid level in the chute. In the conventional system, there is no such liquid communication when the screening device is plugged and hence, the chute liquid level control valve have to be placed in connection with a level tank, normally between the in-line drainer and the level tank.
• the rotary speed of the pockets in the high-pressure feeder can be increased to a speed which is at least up to twice as high as in a conventional feeding system.
• the pump hereinafter called the first pump
• the first pump in the recirculation flow
• the second pump that pumps liquid from the low pressure recirculation flow to the high pressure return liquid flow from the treatment vessel.
• the pump head of the first pump can be added to the pump head of the second pump, whereby the second pump may be one standard pump instead of, as in the conventional system, two standard pumps or one high-pressure pump with several impellers.
• the second pump may be one standard pump instead of, as in the conventional system, two standard pumps or one high-pressure pump with several impellers.
• said recirculation flow that is the volumetric flow that exits the high-pressure feeder on its low-pressure side is related by a factor 0.8-1.5 to the volumetric chip flow which is handled by the high pressure feeder.
• the maximum theoretical volumetric flow can be calculated as the volume of the pockets in the high pressure feeder multiplied with the rotary speed of the high pressure feeder and by a factor two (since the pockets are filled twice in each complete rotation).
• Another way of calculating the volumetric flow is by dividing the incoming chip flow (as measured in a chip meter) by a factor 0.5-0.9.
• a sand trap is installed in said return liquid flow.
• This location has the benefit, as compared to the conventional location in the circulation loop, that the flow is steady, without any essential fluctuations in its velocity.
• the sand trap consists of a cyclone that has to be optimised for a certain flow velocity and will thus operate better in the relatively steady return liquid flow from the treatment vessel.
• the sand trap may be installed in the chute.
• a further advantage is that the sand is not circulated in said recirculation flow on the low-pressure side of the high-pressure feeder, whereby its wearing effect on the equipment is avoided.
• Figure 1 represents a feeding system according to a conventional system.
• Figure 2 represents a feeding system according to a preferred embodiment of the invention.
• Figure 3 represents a feeding system according to an altemative embodiment of the invention.
• Figure 4 shows a tramp material catcher.
• Figure 5 shows the tramp material catcher in figure 4 in the section view A-A.
• Figure 6 shows a typical high-pressure feeder with its pockets.
• FIGURE DESCRIPTION Figure 1 represents a feeding system according to a conventional system.
• Detail 1 in figure 1 denotes a low pressure feeder, which sluices chips, that has been steamed in a previous step (not shown), from atmospheric pressure into a slight overpressure in a chip chute 2.
• the low pressure feeder 1 may be excluded from the system or may be located at an earlier position in the system. In the chute, there are levels of liquid and chips. The chips fall by gravity down into a high pressure feeder 3 through a first opening 3a in its housing.
• the high pressure feeder comprises rotating pockets, whereby a first pocket, via the first opening 3 a, is in open connection with the chute and, via a second opening 3b, which is equipped with a strainer plate, in the housing is connected to a recirculation flow 4 at the same time as a second pocket, via a third opening 3c in the housing, is in open connection with a return liquid flow 5, which comprises liquid that has been separated from the chips in a top separator in the treatment vessel, and, via a fourth opening 3d in the housing is in open connection with a sluicing flow 6 for feeding chips and impregnation liquid to the treatment vessel. Due to the strainer plate in the second opening 3b, chips are to a degree prevented from entering the recirculation flow 4.
• the pocket which is in open connection with the return liquid flow 5 is filled with liquid at a relatively high pressure at the same time as a mixture of chips and liquid, which was present in the pocket, is displaced into the sluicing flow 6.
• this pocket moves into the position of the first opening 3 a, the liquid in the pocket is again displaced by a mixture of chips and liquid from the chute 2.
• the filling degree does however not reach optimum since the strainer plate becomes partially plugged by chips.
• the liquid which has been displaced enters the recirculation flow 4 and is pumped, by a first pump 7, to a sand trap 8, where sand and other particles are removed from the liquid flow. Thereafter, the liquid recirculation flow 4 continues through an in-line drainer 9 and back to the chute 2.
• a branch flow 10 is extracted through a screen in the in-line drainer 9, to prevent any chips that might be present in the flow 4 from entering the branch flow 10, and is introduced in a level tank 11 , in which a certain liquid level is maintained at all times.
• Liquid is pumped, by a second pump 12 which may consist of two or more standard pumps or one high pressure pump, in a conduit 13 from the level tank 11 to the return liquid flow 5 from the treatment vessel, in order to constitute a part of the liquid that displaces the chips in the high pressure feeder.
• the liquid in the level tank 11 has mainly three sources, that is the liquid which is displaced by chips in the high pressure feeder 3, condensate and water from the chute 2 and leakage from the high pressure side to the low pressure side of the high pressure feeder 3.
• To the second pump 12 there may also be added cooking chemicals, especially white liquor.
• the flow of high-pressure return liquid 5 is maintained by a third fluid pump 16.
• the liquid level in the chute 2 is controlled by a chute liquid level control valve 14 which is arranged in the branch flow 10 between the in-line drainer 9 and the level tank 11. If the liquid level in the chute 2 becomes to low, the valve 14 will throttle down, and vice versa.
• the liquid level in the level tank is in its turn controlled by a valve 15 in the conduit 13 between the level tank 11 and the return liquid flow 5.
• the recirculation flow 4 is in reality controlled by the existence of a screening device in the high pressure feeder 3. When the screening device becomes plugged, the first pump 7 does not get any fluid to pump and thus the flow is interrupted.
• FIG. 2 represents a feeding system according to a preferred embodiment of the invention.
• the equipment that is the same as in figure 1 has been denoted with the same reference numbers.
• the high pressure feeder 3 is, according to the invention, in open connection, with respect to both liquid and chips, with the recirculation flow 4', when any of the pockets of the high pressure feeder is in a location which corresponds to an outlet for said recirculation flow 4', that is at the second opening 3b' in the housing.
• the liquid level in the chute can be controlled by a chute liquid level control valve 14' in connection with the second pump 12', or by controlling the rotary speed of the second pump 12', whereby no level tank is needed.
• the in-line drainer is not needed either, since its only function was to prevent chips from entering the level tank where it would accumulate. This means that the recirculation flow 4' can be led directly back to the chute 2.
• This flow is regulated, by a valve 17 or by controlling the rotary speed of the first pump 7', against the flow of chips that is entering the feeding system, which chip flow is measured by a measuring device, for example a so called chip meter screw 18.
• a tramp material catcher 20 is arranged close to the inlet of the first pump 7.
• the design of the tramp material catcher 20 is shown in detail in figures 4 and 5.
• the pump 7 is capable of maintaining a pumping action even if large amount of chips will enter the recirculation flow 4'.
• tramp material in form of bolts, nuts, tools and large stones needs to be separated in order not to destroy the pump 7.
• the tramp material catcher 20 is therefore designed with a pocket 24 in the lower part of the pump inlet.
• the central part of the pump wheel 22 extended, forming a boss 23 member.
• the boss member should preferably extend to such an extent that it could create a swirling motion in the flow 4' above the tramp material pocket 24.
• Tramp material is thus separated by centrifugal forces in the flow 4.
• the pocket 24 could be retrieved via an inspection cover 21, enabling manual extraction of tramp material collected in said pocket.
• Black liquor, BL could also be used in order to flush the pocket clean of any chips.
• the black liquor supply is controlled via valve HS.
• the valve HS is preferably opened automatically upon start of the system. The addition of black liquor will improve establishment of a stable flow in the system. Once the flow is established after a start-up, then the valve HS is closed. The valve HS could also be opened automatically if the rotating pockets of the high-pressure feeder are stuck.
• a branch flow 13' is, via the pump 12' led directly from the recirculation flow 4 to the return liquid flow 5 and is controlled, according to the above mentioned, by the chute liquid level control valve 14' or by controlling the rotary speed of the second pump 12'.
• the first pump 7 and the second pump 12' are coupled in series, whereby one standard pump is sufficient as the second pump 12'.
• Figure 3 represents a feeding system according to an alternative embodiment of the invention.
• the recirculation flow 4" (in this embodiment called a first recirculation flow) is led to the return liquid flow 5 from the treatment vessel and thereby to the high-pressure liquid inlet side of the high pressure feeder 3.
• a second recirculation flow 19 is led from the return liquid flow 5 to the chute 2 for adjustment of the liquid/wood ratio in the chute, and is controlled by the flow control val ⁇ e 17" against the flow of chips that is entering the feeding system.
• the first recir- 10 is led to the return liquid flow 5 from the treatment vessel and thereby to the high-pressure liquid inlet side of the high pressure feeder 3.
• culation flow 4" is regulated, by a chute liquid level control valve 14" or by controlling the rotary speed of the first pump 7", against the liquid level in the chute 2.
• a similar tramp material catcher 20 is located in the inlet of the pump 7".
• the safety pressure switches can be set at comfortable levels, e.g. at pressures above 3 bars, preferably above 5 bars, which allows for stable operation minimising costly unwanted interruptions of the production.
• FIG 6 is a typical valve member 30 for a high-pressure feeder shown.
• the rotating valve member 30 includes at least one, most often four, diametrically through going pockets 31, 32.
• the pocket 31 is exposed to the inlet 42a in the stationary housing 40, then this pocket is filled with chips from the chute 2.
• the pocket 31 closed, and the pocket 32 exposed to the inlet 42b.
• the pocket is flushed with liquor and the chips leaves each pocket in the high pressure feeder via outlets 41a and 41b respectively.
• a strainer plated 50 been used in the outlet 3b' from each pocket, preventing chips from passing through the high-pressure feeder.
• the function of a high-pressure feeder is explained in more detail for example in US 5,236,285, US 5,236,286 or US 4,372,711.
• the flow from the second pump may discharge into many other positions than shown above, e.g. directly into an impregnation vessel, directly into a digester, the pressure side (5) of the top circulation pump (third fluid pump 16) and also on the high pressure side (6) of the HP-feeder. It is also evident that speed control of the pumps may be used instead of conventional drive 11
• the relevant opening in the high-pressure feeder should be designed to prevent chips from stacking up.
• a screening device with slots wider than for instance 25- 30 mm will be included in the scope of the invention, since such a screening device will allow the chips to pass through the opening.
• the relevant opening in the high pressure feeder can be equipped with a screening device with slots narrow enough to make the chips stack up, if the screening device is movable and withdrawn from the opening for a major part of the time. If necessary, that is if the operating conditions otherwise result in an excess of chips entering the recirculation flow, such a screening device could be introduced in the opening just before a pocket is filled up with chips and be withdrawn immediately afterwards, when the pocket proceeds to its high pressure position.
• the skilled man will also realise that instead of controlling certain flows by regulating them against the flow of chips that is entering the feeding system, as described above, the flows can be regulated against the rotary speed of the pockets in the high pressure feeder.
• the device that measures the flow of chips that enters the feeding system may also control the number of revolutions of the pump in the flow to be controlled, instead of controlling a valve in the flow.

Landscapes

• Paper (AREA)
• General Preparation And Processing Of Foods (AREA)
• Processing And Handling Of Plastics And Other Materials For Molding In General (AREA)
• Formation And Processing Of Food Products (AREA)
• Feeding, Discharge, Calcimining, Fusing, And Gas-Generation Devices (AREA)

Priority Applications (7)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20410219

Family Applications (1)

Country Status (11)

Cited By (3)

Citations (2)

• 1998
  • 1998-02-18 SE SE9800476A patent/SE9800476D0/xx unknown
• 1999
  • 1999-02-09 DE DE69941682T patent/DE69941682D1/de not_active Expired - Lifetime
  • 1999-02-09 JP JP2000532585A patent/JP4739518B2/ja not_active Expired - Lifetime
  • 1999-02-09 AT AT99906650T patent/ATE449881T1/de active
  • 1999-02-09 AU AU26505/99A patent/AU2650599A/en not_active Abandoned
  • 1999-02-09 WO PCT/SE1999/000162 patent/WO1999042653A1/en active Application Filing
  • 1999-02-09 CA CA002317750A patent/CA2317750C/en not_active Expired - Lifetime
  • 1999-02-09 ES ES99906650T patent/ES2337532T3/es not_active Expired - Lifetime
  • 1999-02-09 EP EP99906650A patent/EP1056903B1/en not_active Expired - Lifetime
  • 1999-02-09 BR BRPI9907838-4A patent/BR9907838B1/pt not_active IP Right Cessation
  • 1999-02-09 PT PT99906650T patent/PT1056903E/pt unknown

Patent Citations (2)

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