FI74497C - Method of mixing chemicals with pulp of wood and mixer used in the process. - Google Patents

Abstract

Process and apparatus for mixing a wood pulp slurry with a chemical at the consistency at which the slurry exits a washer or the subsequent stem mixer, 7 to 15%. The chemicals would include non-condensable or unsaturated gases such as oxygen, ozone, air, chlorine, chlorine dioxide, sulfur dioxide, ammonia, nitrogen, carbon dioxide, hydrogen chloride, nitric oxide or nitrogen peroxide. Highly superheated steam can also be mixed with the pulp. In the process, the pulp slurry would pass through a mixing zone having a swept area in the range of 10,000 to 1,000,000 square meters per metric ton of oven dry pulp. The optimum is considered to be around 65,400 square meters per metric ton of oven dry pulp. An existing extraction stage within the system may be used as a source of alkali. In an existing extraction stage, the mixer (211) and upstream oxygen line (212) would be placed in the line between the steam mixer (206') and the extraction tower (213'). The oxygen may be inserted into the pulp slurry and mixed with the pulp slurry between a pair of washers (71', 91'). The second washer (91') may be a vacuum, pressure or diffusion washer. The oxygen may be inserted into the pulp slurry and mixed with the pulp slurry between a washer (91') and the subsequent storage tank (110'). Washed wood pulp from a continuous digester (14) may be treated with oxygen in the blow line (19) from the digester (14). Most of the treatment occurs within the mixer (40). Following mixing, the pulp may be taken to a subsequent process, a diffusion washer (24), or to a storage tank (24). The pulp is treated several times during a sequence. Some sequences are O-X-O and O-O-X-O in which X may be chlorine, chlorine dioxide, a combination of chlorine and chlorine dioxide and a hypochlorite, a peroxide or ozone. The sequence may be followed by a D stage. Other systems and specific mixer designs are also disclosed.

Description

j 74497

A method of mixing chemicals with wood pulp and a mixer used in the method

The invention relates to a method for mixing a chemical with wood pulp and to a mixer used in the method.

Pulp production means the conversion of wood chips or other particulate wood into a fibrous form. Chemical pulping requires the wood chips to be boiled in solution with the chemical and involves the partial removal of a colorant, such as wood-associated lignin.

Bleaching refers to the treatment of cellulosic fibers to remove or modify the colorant associated with the fibers so that the fibers better reflect white light.

The following standard symbols are used for pulping and bleaching: S = sulphite 20 K = sulphate

So = soda ash C = chlorine H = sodium or calcium hypochlorite E = alkali extraction, usually with sodium hydroxide 25 D = chlorine dioxide P = alkaline peroxide O = oxygen A = acid pre-treatment or post-treatment Consistency refers to the number of pulp fibers in the slurry, expressed as a percentage of solvent usually water, by total weight. It is sometimes called mass content.

The consistency of the pulp depends on the type of dewatering equipment used. The following definitions are based on those presented in Rydholm: Pulping Processes, 2 74497

Interscience Publishers, 1965, pp. 862-863 and TAPPI Monograph No. 27, The Bleaching of Pulp, edited by Rapson, The Technical Association of Pulp and Paper Industry, 1963, pp. 186-187.

5 The low consistency is 0-6%, usually between 3% and 5%. It is a suspension that can be pumped with a standard centrifugal pump and is available using thickeners and filters without compression rollers.

The average density is 6-20%. 15% is the dividing point in the middle-10 consistency range. A consistency of less than 15% can be achieved by filtration. This is the massless consistency as it exits the vacuum drum filters in the brown pulp washing system and bleaching system. The consistency of the sludge 15 leaving the scrubber, either the post-cooking pulp scrubber or the bleaching scrubber, is 9-13%. Above 15%, press rolls are required for dewatering. Rydholm states that the usual range for the average consistency is 10-18%, while Rapson states that it is 9-15%. The slurry must be pumped with a special coil even when it is still a cohesive and liquid phase at higher temperatures and under slight compression.

The high consistency is 20-40%. Rydholm states that the normal range is 25-35% and Rapson states that the range is 20-35%. These consistencies can only be achieved with presses. The fibers completely absorb the liquid phase and the pulp can only be pumped over very short distances. For practical purposes, it is non-pumpable.

The amount of mass is expressed in several different ways.

The oven-dry mass is considered to be free of moisture 30, i.e. oven-dry. Its value is determined by drying the pulp in an oven at a temperature of 100 to 105 ° C until the weight of the pulp remains unchanged. It is generally considered to have reached a constant weight after 24 hours in the oven.

The air-dry mass is assumed to contain 10% moisture. One ton of air-dry pulp corresponds to 0.9 tonnes of uu-dry pulp.

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The following describes a typical pulp mill and associated oxygen bleaching systems and compares the present invention to such a mill.

Figure 1A-1C is a diagram of a typical pulp mill.

5 At the factory, the equipment for transporting chips or pulp from one operation to another depends on the consistency of the pulp and the location of the equipment. The means of transport may be a conveyor or a downcomer if the consistency is too high for the pulp or chips to be pumped, or a line if the pulp can be pumped. The wood chips 10, process water 11, steam 12 and pulping chemicals 13 are introduced into the digester 14. The wood chips 10 can be treated before being introduced into the digester 14. This is optional. Examples of such treatment are the pre-steaming of the chips in a steaming vessel or the impregnation of pulp chemicals in the chips in the impregnation vessel before the chips are introduced into the digester. The chemicals 13 depend on the method used, be it a sulfate, sulfite or soda method, and the digester 14 can be either batch or continuous. The figure shows a cooker. The chips are boiled under 20 suitable conditions in a digester. These conditions, which depend on the type of chips and the type of pulp used, are well known.

Products from the pulping process include delignified or partially delignified wood chips, used pulping chemicals 25, and lignin and carbohydrate products that have been removed from the wood chips during the pulping process. The processing of the chips after cooking depends in part on the type of cooker used. Most of the pulping chemicals and lignin products used are removed from the chips before further processing. In the pre-30 bed, the chips are washed in the washing compartment of the cooker. This is indicated by the process water 15 entering the washing stage of the digester 14 and the outlet stream 16 leaving it. The effluent stream 16 consists of lignin and carbohydrates removed from the chips during the pulping process and the pulping chemicals used. This effluent is transported to a treatment plant. In the case of a sulphate pulp of 4,74497, this would be a recovery system in which the liquid is incinerated to recover pulping chemicals for reuse.

This washing would not take place in a batch cooker. In a batch system, all washing would take place in a subsequent post-cooking pulp washing system.

After this treatment, the chips pass from the digester 14 through a dozer line to a storage or buffer tank 22. In pulp mills, it is common for there to be 10 storage tanks between different processes, so that the entire mill does not stop if one mill department stops. The storage tank 22 is one such tank. It would be between the pulping step and the subsequent washing or bleaching steps. The storage tank 22 is open to the atmosphere and is thus at atmospheric pressure.

The tank 22 may be in the position of a diffuser storage tank. Diffusers are described in Rydholm, Pulping Processes, Interscience Publishers, 1965, pages 725-730 and shown in Figure 10.14 on page 728. Diffusers would be followed by a storage tank.

20 The material that passes through the butt pipe is a slurry containing the remaining lignin and carbohydrates, spent pulping chemicals, and fibers formed from the chips as they are pushed out of the digester. The chips turn into fibers when the pressure on the chips is partially released, 25 usually at the outlet of the digester 14. The slurry is still under low pressure to move it through the butt pipe. If the kettle is a cooker, the additional fiberization can be done with a grinder or grinders in the butt line. The refiners fiberize large particles that have not shrunk to fibers ai-30 earlier in the process. This diagram shows two refiners - 18 and 19. In a two refiner system, the first refiner 18 performs coarse refining and the second refiner 19 performs fine refining. Grinders are optional. They are usually found in a kraftliner factory. The digester 35 would not normally have grinders in the butt line in the bleached pulp mill. Nor would they be used with a batch cooker.

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The dozer line is shown in three parts - part 17 between the digester 14 and the refiner 18; part 20 between refiners 18 and 19; and a portion 21 between the refiner 19 and the storage tank 22.

From the storage tank 22, the fibers and liquid are conveyed by the pump 23 through the line 24 to the scrubbers and sorters. The system is described by monitoring the pulp through the system and then monitoring the wash water through the system.

The pulp slurry is first passed to brown pulp washers 28 where the remainder of the lignin and chemicals are removed from the fibers 10. The figure shows four washers. This is the amount normally used with a batch digester. The Fri-favorite in the cauldron would replace the first two brown pulp washers. Each of these scrubbers is usually a vacuum or pressure drum scrubber or a vacuum or pressure drum filter and each has a similar operation. The operation of a vacuum or pressure drum washer is described. However, some of the scrubbers may be diffusers. In the diffuser, the pulp slurry is not diluted before entering the scrubber.

The pulp slurry line 24 enters the vat 30 of the scrubber 31. The vacuum drum 32 rotates across the vat and the vacuum absorbs the fibers in the slurry onto the outer surface of the filter drum and holds the fibers in mat form while sucking liquid or filtrate through the filter cloth into the vacuum drum. A rotating drum carries a group of 25 non-fibrous vat spray nozzles that spray dilute filtrate onto the mat to displace liquid from the mat. The vacuum also sucks this displaced liquid into the inner tubing of the drum. From the scrubber, either from the brown pulp scrubbers described herein or from the scrubber scrubbers described later, the consistency of the carpet leaving is usually 8-15%.

The pulp mat 33 is removed from the surface of the drum 32 with a scraper blade, support wires or strips between the drum or mat, rollers or some other conventional means 35 and introduced into the cone 50 of another brown pulp washer 51. Again, the fibers adhere to the vacuum drum 52. 74497 from the vacuum drum 52 and applied to the vat 70 of the brown pulp scrubber 71. The operation of this scrubber is similar to the others, the vacuum drum is 72 and the mat 73. The mat 73 is conveyed to the vat 90 of the brown pulp washer 91. The operation of this scrubber is again is 92 and carpet 93.

From the brown pulp scrubbers, the pulp mat 93 is introduced into the storage tank 110 by means of a thick pulp pump 96. In the lower part of the tank 110, the pulp is diluted and then conveyed via line 111 by a pump 112 to sorters 113 for removing larger fiber bundles and branches. The fiber bundles and branches 114 are transported by a transport device suitable for further processing.

The pulp 115 is conveyed from the screeners 113 to the cone 120 of the thickener 121, where the additional water is removed. The operation of the thickener 15 is similar to that of the scrubbers. Washing sprays are used or not used in the thickener. The vacuum drum is 122 and the pulp mat is 123. The pulp 123 is conveyed by a thick pulp pump 126 to a high pressure storage tank 140 where it is stored until bleached.

Liquid or filtrate from the vat 120 and mat 123 flows through a tubing that runs radially from the empty chambers on the surface of the vacuum drum 122 to the tube in the central axis of the rotating drum. This liquid or filtrate passes through a central tube and an external conduit 128 to a filtrate storage tank, i.e. a closure tank 129. The tank 129 is termed both a storage tank and a closure tank because it serves both to store filtrate for further use and to close the vacuum drum 122 from the outside atmosphere.

30 The filter tank 129 can be treated in many ways. Many of the uses can occur simultaneously. Although the following description is specific to the effluent from the tank 129, it also describes how the effluent from any scrubber in the brown pulp washing system 28 could be treated.

The following description describes how the effluent from each scrubber is handled.

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First, the filtrate from tank 129 is reused to reduce the consistency of the pulp slurry, which either enters thickener 121, enters sorters 113, or exits storage tank 110. Line 130 transports filtrate to lines 131, 5 133, and 135. Line 131 and pump 132 return the filtrate. to the sorted pulp 115 to reduce the consistency of the fibrous slurry entering the cone 120 to about 1.5%. Line 133 and pump 134 take the filtrate back to line 111 to reduce the consistency of the pulp slurry entering the screeners 113 to 0.2-2%. Line 135 and pump 136 bring the filtrate back to storage tank 110 to reduce the consistency of the fibrous slurry exiting the tank to about 5%. Second, the filtrate not used for dilution can be taken to the effluent treatment system via line 130 and effluent 15 via this line. This treatment involves combining the effluent with the effluent in line 16 or introducing the effluent directly into the broth recovery system. It should be understood that in the batch digester system, the digester effluent is completely recovered from the post-cooking pulp washing system, while in the feeder system, only a portion of the digester effluent is recovered from the brown pulp scrubbers.

Any remaining filtrate would be treated as a effluent unless a countercurrent wash is used, which is described below. Part of the filtrate can be treated as an effluent even if countercurrent washing is used.

Third, the filtrate from the tank 129 can be used as wash water in the brown pulp wash system 28 in the countercurrent wash system. In this system, the flow of filtrate is opposite to the flow of pulp. Line 137 and pump 138 return the filtrate to the brown pulp scrubber 91 for use as wash water. The filtrate is sprayed onto Massama with spray nozzles 95 and displaces the liquid 35 in the mat. This filtrate can also be sprayed onto carrier fabrics, strips or rolls after the pulp mat has been separated from them and to remove any pulp fibers stuck to the fabrics, strips or rolls of 8,74497 rollers if water is used for this purpose instead of air. This is done with a cleaning washer 94. Additional water is needed to replenish the filtrate. This is obtained from process water line 97.

The flow of the filtrate through the brown pulp scrubber 91 is similar to the flow through the thickener 121. The liquid, either from the mat or the vat, is introduced via internal piping to line 98 and through line 98 to the filtrate storage tank, i.e. the closure tank 99. Again, the filtrate from the closure tank 99 can be treated in many ways. Line 100 could carry it to drain line 29. Line 101 and pump 102 could carry filtrate to pulp 73 to reduce the consistency of the pulp slurry to 1.5-3.5% when it enters vat 90. Line 103 and pump 104 could carry filtrates to brown pulp. -15 sanitary washers 71 for use as wash water.

The process in the brown pulp washers 71, 51 and 31 is for the most part similar to the process in the brown pulp washer 91, so the parts are numbered in the same way. The spray heads are 75, 55 and 35, respectively. The cleaning washing-20 devices are 74, 54 and 34, respectively. The filtration lines are 78, 58 and 38 and the filtrate storage or sealing tanks are 79, 59 and 39. The filtration lines from the sealing tanks to the outlet line 29 are 80, 60 and 40. .

The slurry entering one of the types 70, 50 or 25 should have a consistency of 1.5 to 3.5%. The lines and pumps that also bring the filtrate into the pulp to reduce the consistency of the slurry entering the vat are 81 and 82, 61 and 62, and 41 and 42, respectively. Counter-current scrubbers and pumps are 83 and 84 and 63 and 64.

In the brown pulp scrubber 31, line 43 and pump 44 convey filtrate to storage tank 22 to reduce the consistency of the pulp slurry at the bottom of the tank to 2-3.5% before it leaves the tank.

In each brown pulp scrubber, it is possible that additional process water is needed to replenish the filtrate used as wash water. Lines 77, 57 and 37 are for this purpose. These lines would supply all 9,74497 washes of wash water to the individual washers if the countercurrent system described above is not used and co-current washing is used instead.

The washed pulp that has passed through the brown pulp wash-5 system 28, screeners 113, and thickener 121 remains in the storage tank 140 until it is conveyed to the bleaching system.

The bleaching process shown in Figure 1 is also described by monitoring the pulp flow through the bleaching system from the pulp to the bleached pulp and then monitoring the wash water from its input to the process up to the bleaching plant effluent. The specific bleaching series described is D EDED. The process conditions are taken from the above-mentioned c TAPPI special study The Bleaching of Pulp.

15 There are many other bleaching kits that can be used. Lists of these series can be found in the manuals. Generally, the first step is the chlorine step and the subsequent steps use chlorine dioxide, hydrogen peroxide or hypochlorite. Between these steps are al-20 potassium extraction steps.

The consistency of the pulp stored in the high pressure tank 140 is normally about 9-15%. This pulp slurry is conveyed from tank 140 via line 141 to tank 146 by pump 142. The pulp in line 141 is diluted with additional water or filtrate 25 to a consistency of about 5%. In mixer 144, line 141, the slurry is mixed with chlorine dioxide from line 145 as the D-stage of the first bleaching stage D. If the first step is c purely the chlorine step, then this step would be omitted. The treated dilute slurry enters a storage tank 146, 30 where chlorine dioxide reacts with the unbleached pulp. The size of this tank depends on the amount of pulp to be treated and the time of chlorine dioxide treatment. This initial treatment normally takes 1-5 minutes. The slurry exits the tank to line 150 and is treated with chlorine.

35 Chlorine from line 151 and process water from line 152 are mixed in a vacuum cleaner 153 and diluted chlorine flows in line 154 to a mixer 155 where chlorine is mixed with dilute pulp slurry 71497 in line 150. Treated slurry is transferred by pump 156 through line 150B to chlorine bleach tower 157. Tower 157 is rated with the substance in an unbleached mass. This pi-5 addition or reaction time depends in part on the water temperature. At the minimum temperature, the TAPPI study suggests a retention time of about 45-60 minutes for sulfite pulp and 60-90 minutes for sulfate pulps. The treated slurry exits the tank 157 and is conveyed through line 158 and pump 159.

The slurry in line 158 is combined with additional water or filtrate to reduce the consistency to about 1-1.5%. This dilute slurry flows into the vat 160 of scrubber 161. Again, a vacuum drum scrubber or filter is shown in the figure. The operation of this washer is similar to that of brown pulp washers.

15 The vacuum drum 162 rotates in the hoe. The vacuum sucks the fibers in the slurry onto the outer filter surface of the drum and holds them against the surface to form a mat while sucking liquid or filtrate through the filter cloth into the inner tubing of the vacuum system in the drum for removal as an outlet stream. A rotating drum 162 carries a group of non-fibrous vats past the spray heads that spray water or dilute filtrate onto the mat to displace the reaction products and unreacted chlorine adhering to the mat.

The pulp mat 163 is removed from the surface of the drum 162. The Off-25 feeder is the same as for brown pulp washers - scraper blade, carrier wire or - strips between the drum and the mat, rollers or in some other usual way. The pulp mat 163 is transferred to a mixer 166. This transfer is usually by gravity through a downcomer to the scrubber 30.

Before leaving the scrubber 161, the pulp mat 163 is impregnated with an alkaline solution or an alkali extraction solution from line 167. Usually sodium hydroxide solution is used. The alkali solution is applied to the mat just as it exits 35 from the vacuum drum 162 so that the solution penetrates the pulp mat but does not pass through the mat into the scrubber effluent. The amount of alkali added, expressed as sodium hydroxide, is 0.57% by weight of the oven dry matter. Alkali can be added to the pulp in a steam mixer 166 instead of a scrubber 161.

The mat treated in steam mixer 166 is mixed with steam due to line 168 to raise the pulp temperature n.

5 to 62 ° C. The heated slurry is conveyed through line 169 to the extraction tower 173 by a high pressure pump 170a. In some cases, transfer to the extraction tower is by gravity. The flow in the extraction tower can be up or down. A high pressure pump 170 for both the upstream tower and the downstream 10 back tower may be located at the bottom of the tower. The pulp would then be taken to the upper end of the downstream tower by an external line. Placing the pump in a plant is a matter of convenience. Pump supply and Access to the pump for maintenance are important considerations. The slurry remains in tower 173 to allow the extraction solution 15 to react with the chlorinated materials and extract from the pulp. This takes one to two hours.

Before leaving the extraction tower, the pulp slurry is mixed with water or filtrate in dilution zone 174 to reduce its consistency to about 5%. The slurry is conveyed by line 175 and pump 176 from dilution zone 174 to washer 180 of scrubber 181. Washer 181 is shown in the figure and is described as a vacuum or pressure drum scrubber, but may be a diffuser. As it passes through line 175, the slurry is further diluted with water or filtrate until it has a consistency of about 1 -1.5% when it enters the cone 180. The operation of scrubber 181 is similar to that of scrubber 161. The fibers adhere to the rotating drum 182, wash, and remove as a mass mat 183.

The pulp is then transferred to a steam-30 steam-30 mixer 186. This transfer can again be a gravity drop through a downcomer. Before leaving the scrubber 181, the mat 183 is treated with a small amount of alkali from the conductor 187. Usually sodium hydroxide solution is used. It is added to the mat at a point with a drum that sal-35 dissolves the solution remaining on the mat and does not pass through the filtrate. The purpose of this treatment is not further extraction, but to adjust the pH of the pulp before treating it with chlorine dioxide. The pH of the pulp should be between 5-7, preferably 6, optimal for brightness when bleached with chlorine dioxide. Alkali can be added in the steam mixer 186 instead of the scrubber 181. In the steam mixer 186, the pulp 183 is mixed with the steam 5 from line 188. The consistency of the pulp is about 1 percentage point lower than when leaving the scrubber as it exits the steam mixer.

The pulp exits steam mixer 186 and is conveyed through line 189 by pump 190 to mixer 191, where it is mixed with chlorine dioxide from line 192. It then enters chlorine dioxide tower 193. This tower is usually an upstream-downstream tower. The retention time in the tower is long enough to allow chlorine dioxide to react with the pulp. The reaction is almost complete after one hour, but is normally continued for up to four hours. Thus, the detention time in the tower is usually four hours. Before leaving the tower, the slurry is diluted to a consistency of about 5% in dilution zone 194. It is also treated with a small amount of sulfur dioxide or alkali due to 197.

Sulfur dioxide or alkali reacts with any excess chlorine dioxide so that no free chlorine dioxide is removed from the scrubber and it is not present in the pulp leaving the scrubber.

This diluted slurry is then introduced in line 195 25 and by pump 196 to scrubber 200 of scrubber 201. As it passes through line 195, the slurry is again diluted to a consistency of about 1 to 1.5% when it enters tank 200 and is treated again with sulfur dioxide from line 198. The pulp adheres to the vacuum drum 202 and the reaction products and unreacted bleaching chemicals are washed therefrom prior to removal as pulp 203. This pulp is transferred to a second stage steam mixer 206, usually by gravity drop through a downcomer. Again, sodium hydroxide is added from line 207 by scrubber 201 or the pulp mat 203 treated in mixer 206 is mixed with steam from line 208. This slurry is then conveyed in line 209 by pump 210 to extraction tower 213. Conditions in the extraction step are the same as 13,74497 in the first extraction step. In the tower, the flow can be down or up.

After a suitable residence time, the pulp enters the dilution zone 214 and its consistency is reduced to about 5%.

The pulp is then passed through line 215 by pump 216 to vane 220 of scrubber 221. Washer 221 is also shown in the figure and is described as a vacuum or pressure drum scrubber, but may also be a diffuser. The mass is again diluted by approx.

To a consistency of 1 to 1.5% before entering the vat. The slurry adheres to the vacuum drum 222 and is washed and removed as a pulp mat 223. If necessary, the pH of the pulp can be adjusted by treating the mat with sodium hydroxide from line 227. This can be done with a drum 222 or a steam mixer 226.

The pulp enters the last chlorine dioxide stage. The Olo-15 ratios and flow at this stage are similar to those at the first chlorine dioxide stage. The pulp is dropped or taken to a steam mixer 226 and mixed with steam from line 228. The slurry is passed through line 229 by pump 230 to mixer 231, mixed with chlorine dioxide from line 232 and fed to chlorine dioxide tower 233, shown as an upstream-downstream tower where it remains 1-4 hours . The pulp then enters dilution zone 234, where its consistency is reduced to about 5%. It is also treated with a small amount of sulfur dioxide due to 237 to remove all 25 excess chlorine dioxide.

The slurry is removed from the dilution zone 234 via line 235 by pump 236. During its passage through line 235, the pulp is again treated with additional sulfur dioxide or alkali from line 238 to remove any free chlorine dioxide and further diluted to a slurry consistency of about 1-1.5% scrubber 241 to vat 240. It is assembled with a vacuum drum 242, washed, and removed from the bleaching system as a bleached pulp 243.

The mat usually adheres the pulp to the wire or strips that carry the pulp mat from the scrubber and it is necessary to wash these fibers from the wire or strips into the bath before they come in contact with the new fibers. This can be done with 14 74497 cleaning washer 164 with washer 161, cleaning washer 184 with washer 181, cleaning washer 204 with washer 201, cleaning washer 224 with washer 221, and cleaning washer 244 with washer 241. Air can also be used.

The flow of liquid through the scrubber is similar to that of brown pulp scrubbers. The wash water is sprayed onto the carpet with shower heads. This water displaces the liquid adhering to the mass mat on the drum. The displaced fluid passes through the internal tubing of the rotating vacuum-10 drum to a line in the central axis of the drum. Here it combines with the liquid absorbed into the drum from the scrubber type. This combined liquid passes outwardly through the center tube of the drum and through an external conduit to a closure or storage tank which maintains a vacuum in the drum 15 by forming a barrier between the vacuum interior of the drum and the pressure outside the body.

In scrubber 161, process water from nozzle heads 251 passes through the central axis of vacuum drum 162 and outwardly through external conduit 252 to sealing or storage tank 253. Sprayer heads 181 spray nozzles are 271, outer tube is 272 and sealing or storage tank is 273. In scrubber 201, nozzle heads are already 291. is 292 and the closure or storage tank is 293. In the scrubber 221 the spray heads are 311, the outer line is 312 and the closure or storage tank is 313 and in the scrubber 241 the spray heads are 331, the outer line is 332 and the closure or storage tank is 333.

The routes traveled by the filtrate after leaving the closure or storage tank are also the same as the routes in the brown pulp scrubbers.

30 First, the filtrate is used to dilute the sludge in a washing step or tower.

For example, the filtrate would dilute the pulp slurry that is transported to the vat. The filtrate from the sealing tank 253 of the chlorine stage scrubber 161 would be passed through line 255 and pump 256 to line 158 for use in diluting the pulp slurry to cone 160. Similarly, line 275 and pump 276 and line 227 and pump 278 take the sludge from the seal tank 273 of the first stage 74497 of the leach 182 to the line 175 to dilute the filtrate; line 295 and pump 296 and line 297 and pump 298 take filtrate from the feed tank 293 of the first chlorine dioxide stage scrubber 201 to line 195 to dilute the slurry into the vat 200; line 315 and pump 316 and line 317 and pump 318 deliver filtrate from the sealing tank 313 of the second stage scrubber 221 to line 215 to dilute the sludge to dilute the vat 220; and line 335 and pump 336 and line 337 and pump 338 take 10 filtrate from the shut-off tank 333 of the second chlorine dioxide scrubber 241 to line 235 to dilute the slurry into the vat 240.

In the chlorine stage, line 259 and pump 260 also carry filtrate to line 141 to dilute the pulp from the high pressure stock.

In the extraction and chlorine dioxide steps, the filtrate is also fed to dilute the sludge in question. phase tower in the dilution zone. In the first extraction stage, the filtrate from the shut-off tank 273 is conveyed to the dilution zone 174 by line 281 and pump 282. In the first chlorine dioxide stage, line 301 and pump 302 convey filtrate from shut-off tank 293 to dilution zone 214. and in the second chlorine-dioxide stage, line 341 and pump 342 direct the effluent from the shut-off tank 333 to the dilution zone 234.

Second, the filtrate that is not reused for dilution is removed as an effluent or for further processing via line 254 from tank 253, line 274 from tank 273, line 294 from tank 293, line 314 from tank 313, and line 334 from tank 333. The effluent from the chlorine stage scrubber 161 is separate other scrubbers due to its high chlorine or salt content and its higher residual content. The other lines - 274, 294, 314 and 324 - end in the discharge line 3 50.

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All remaining filtrate would be treated as an outflow unless countercurrent washing was used. Part of the filtrate can be treated as an effluent even if countercurrent washing is used.

In the countercurrent scrubbing system shown, the scrubbing water for the second chlorine dioxide scrubber 241 is process water from line 330; the wash water for the second extraction scrubber 221 is partially or completely filtrate from the second chlorine dioxide scrubber 241 fed from the shut-off tank 333 via line 10 343 and pump 344; the wash water for the first chlorine dioxide scrubber 201 is partially or completely filtrate from the second extraction scrubber 221 fed from the seal tank 323 by line 323 and pump 324; the wash water for the first extraction scrubber 181 is partially or completely filtrate from the first chlorine dioxide scrubber 201 fed from the seal tank 293 via line 303 and pump 304; and the scrubbing water for the chlorine scrubber 161 is partially or completely filtrate from the first extraction scrubber 181 fed from the seal tank 273 via line 283 and pump 284. All excess 20 wash water would be fed through lines 250, 270, 290 and 310. These lines would supply all the wash water to the individual scrubbers unless a countercurrent system is used and co-current scrubbing is used instead.

Chemical, water and steam feeds to the system are shown at the top of Figure 1. Process water is fed through line 360 to various lines that supply water to the process.

Line 351 to cooker lines 11 and 15, lines 37, 57, 77 and 97 for brown pulp scrubbers 28, line 152 to chlorine vacuum 153 and lines 250, 270, 290, 310 and 330 to bleach-30 system scrubbers. Chlorine is fed through line 361 to line 151. Alkaline line 362 supplies dilute alkali to lines 167, 187, 207, and 227. It is normally a 5-10% solution before entering line 362. Chlorine dioxide line 363 supplies chlorine dioxide solution to lines 145, 192, and 35,232. Steam is supplied through line 364 to steam lines 12, 168, 188, 208 and 228. Sulfur dioxide is supplied to lines 197, 198, 237 and 238 via line 365.

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Methods for measuring the utility and efficiency of a pulping or bleaching process include pulp yield, physical properties of the pulp, lignin removal rate of the pulp, brightness of the pulp, and cost to obtain the pulp.

Yield can be measured in two ways. The first is the weight of carbohydrates and lignin that the unit produces wood. The sorted yield is closely related to and proportional to this chemical recovery. A high yield of species-10 means that the chemical recovery is high and a low sorted yield means that the chemical recovery is low. Another measurement of yield is fiber yield calculated by weight per unit of wood. The reject, i.e., the branch mass, is proportional to and inversely proportional to the fiber yield. A high reject level means that the fiber feedback is small and a low reject level means that the fiber feedback is large. The total yield is the sum of these two yields. Ideally, the situation would be one where the chemical feedback is high and the fiber feedback is high, as evidenced by the high sorted yield and low branching mass level.

Physical properties include permeability, puncture, tear, folding, breaking length, density, and viscosity. The pulp samples are ground in a PFI machine, either a certain number of revolutions and a permeability is determined or to a specified permeability and the time to this permeability is determined. The permeability of the pulp, Canadian Standard Freeness (CSF), is determined by the TAPPI standard method T 227 M-58, corrected in August 1958. The ground pulp is tested for puncture, tear, refraction, breaking length, and density. Puncture is a numerical value obtained by dividing the puncture strength in grams / cm by the basis weight of the sheet in grams / m and is determined by the TAPPI Standard Test T 220 M-60, 1960 Revised Tentative Standard method. This test is also used to determine rupture. The tear is a numerical value of 35 and is 100 e / r, where e is the force in grams required to tear a single sheet and r is the weight of the sheet per 2 surface units in grams / m. Folding, breaking length 74497 18 3 in meters and density in grams / cm are determined by the TAPPI Standard Test T 220 OS-71 method. The viscosity of the pulp is expressed in centipoise and is determined by the standard method TAPPI Standard Method T 230 SU-66.

5 There are two main types of measurement to determine the completeness of a pulping or bleaching process, the degree of lignin removal and the brightness of the pulp. There does not appear to be any correspondence between the two, since the delignification factor is a measure of the residual lignin in the pulp and the brightness 10 is a measure of the reflectivity of the pulp sheet.

There are several methods for determining the degree of lignin removal from pulp, but most are variations of the per-manganate test.

The normal permanganate test gives a cubic centimeter of permanganate-15, i.e. a K-value of 0,1 N potassium permanganate solution, which 1 g of oven-dry mass is consumed under the specified conditions. It is determined by the TAPPI standard test T-214.

The number of pieces is similar to the number of permanganate, but it is measured under carefully controlled conditions and corrected to be equivalent to 50% of the consumption of the permanganate solution in contact with the sample. The test gives the degree of lignin removal to the masses from a wider delignification range than the permanganate number. It is determined according to the TAPPI standard test T-236.

PBC is also a permanganate test. The test is as follows: 1. Slurry about 5 g of the hand-pressed mass into a 600 ml beaker and remove any head fragments. 2. Form a test sheet in a 12.5 cm Buchner funnel, wash with 500 ml of additional water. The filter paper is removed from the pulp.

3. Dry the test sheet for five minutes at 99-104 ° C.

4. Remove the test sheet from the drying oven and weigh 35,426 g. This step should be done in a constant time of approx. 45 seconds to ensure constant humidity, as the dry mass absorbs more moisture.

19 74497 5. Slurry the weighed mass sample into a 1 liter beaker containing 700 ml of tap water at 25 ° C.

6. Add 25 ml of 4N sulfuric acid and then 25 ml of 0.1000N potassium permanganate. The timer is started when the addition of permanganate begins.

7. Stop the reaction after exactly five minutes by adding 10 ml of 5% potassium iodide solution.

8. Titrate with 0,1000N sodium thiosulphate. A starch indicator is added near the end of the titration when the solution 10 turns oily. The end point is reached when the blue color disappears.

When performing the test, thiosulfate should first be added as quickly as possible to prevent the release of free iodine. During the remainder of the titration, thiosulfate-15 should first be added as rapidly as possible to prevent the release of free iodine. During the remainder of the titration, thiosulphate is added drop by drop just until the blue color disappears. The titration should be completed as quickly as possible to prevent reveration of the solution.

The PBC figure represents the amount of chlorine in pounds required to completely bleach 100 pounds of air-dried pulp at 20 ° C in a single theoretical bleaching step and is equal to the ml of potassium permanganate consumed as determined by subtracting the ml of thio sulphate consumed per ml of added potassium permanganate. ml chapter.

Many variables affect this test, but the most important are sample weight, reaction temperature, and reaction time.

30 There are also numerous methods for measuring the brightness of pulp. It is usually a measure of reflectivity and its value is expressed as a percentage on some scale. One standard method is GE brightness, expressed as a percentage of the maximum GE brightness, determined by the TAPPI Standard Method TPD-103.

Another measure of brightness or delignification is the opacity of the fiber. Opacity is determined as a percentage of the standard method using the TAPPI Standard Test T 425 OS-75.

20 7 4 4 9 7

The price of the pulping process is measured by both the cost of capital and the cost of working chemicals, in which case the cost of capital is the cost of the plant and equipment and the cost of operation is the chemical, raw material and labor costs of using the process.

The capital cost of the factory is ovar high because large containers are needed to store the chips or pulp during each long process step. For example, The Bleaching of Pulp states that the reaction times are 45-90 minutes for the chlorine bleaching step, 1-8 hours for the hypochlorite bleaching step, 1-4 hours for the chlorine dioxide bleaching step, and 1-2 hours for the extraction step. The size of the tower depends on the retention time, the production volume, the effective tower volume, the consistency, the degree of sealing and the uniformity of the mass flow. 15 Rydholm, cited above, shows that the space requirement per tonne of pulp in a container varies from three to fifteen cubic meters, depending on the consistency and degree of filling. Rydholm proposes a minimum of 7.5 m / ton of pulp and states that 7-8 m / t of pulp is normal for medium consistency operations. This is probably calculated on the basis of the air-dry mass, which is the usual basis at the factory.

With this in mind, we now see how researchers have tried to add oxygen to the pulping and bleaching process or to replace parts of the system with oxygen treatment. 25 A constant concern was the poor solubility of oxygen in water and its poor transfer from the gas phase into the liquid phase and the fiber. Common solutions to these problems have been high pressures, high oxygen concentrations, high pulp densities, or special vessel shapes to promote oxygen transfer to the fiber.

Two papers discuss the use of oxygen in a brown pulp washing system. These are those of Jamieson et al. the text "Integration of Oxygen Bleaching in the Brownstock Washing System", Svenska Papperstidning, No. 5, 35 1973, pages 187-191; and an article describing the actual oxygen system used in a brown pulp washing system, Jamieson, et al. "Advances in Oxygen 21 74497

Bleaching III - Oxygen Bleaching Pilot Plant Operation ", TAPPI November 1971, Vol. 54, No. 11, pages 1903-1908. Each of these systems requires a cylinder press prior to the oxygen step to obtain a pulp consistency of 5 to 30% prior to treatment with oxygen.

Other papers on this process include Jamieson, et al., "Advances in Oxygen Bleaching," TAPPI, November 1971, Vol. 54, No. 11, pages 1903-1908; Jamieson, et al .: "Mill Scale Application of 10 Oxygen Bleaching in Scandinavia", 1973 TAPPI Alkaline

Pulping Conference Publication, pages 231-238; and Fary, et al., "Oxygen Bleaching at Chesapeake Corporation," 1973 Alkaline Conference.

This system, Modo-Cell's Modo-CIL system, 15 has also been described in a number of patents and writings.

The system is described in three U.S. patents. Schleinofer, U.S. Patent 3,703,435, issued November 21, 1972, describes a flotation device for an oxygen reactor. Engström, U.S. Patent 3,668,063, issued June 6, 1972, discloses a method for removing entrained air. Engström et al., U.S. Patent 4,022,654, issued May 10, 1977, describe a new reactor design. These all require large consistencies. The consistency range of the first is 10-50%, preferably 15-30%. The second mentions 20% and the third requires a consistency of 18-40%. 25 it states that consistencies in the range of 3-16% were used in the laboratory, but these consistencies would not allow good mixing of oxygen and pulp without excessive energy for mixing. It also requires time from five minutes to one hour. Everyone requires great pressure. Because 30 of them are all high pressure reactors, they are expensive.

Various preservatives have been used to prevent or reduce the deterioration of pulp quality due to oxygen. There are numerous patents dealing with various preservatives that could be used. Examples include Robert et al., U.S. Patent No. 3,384,533, issued May 21, 1968; Noreus et al., U.S. Patent No. 22 7 4 4 9 7 3 652 386, March 28, 1972; and Smith1 in et al., U.S. Patent No. 3,657,065, issued April 18, 1972.

The subject of concern has also been channeling of the oxygen in the system and various ways to prevent channeling 5 is proposed. Roymoulik et al., U.S. Patent No. 3,832,276, issued August 27, 1974, and Phillips U.S. Patent No. 3,951,733, issued April 20, 1976, mention this problem and suggest solutions.

The process described in these patents requires 10 pulps with a consistency of less than 10%, preferably about 2-6% and very preferably 3-4%. The pulp is mixed with oxygen in a high shear device and the slurry is taken to a vessel. The slurry rises up into the container. The slurry rises upward through the vessel. No actual mixing of the fibers takes place as they travel upwards and the pressure on the pulp gradually decreases. The maximum pressure difference is between one and 10 atmospheres. This is preferably done in a bleaching tower with a height of 40 to 300 feet (12.2 to 91.4 m).

20 "In general, about 5-120 minutes is sufficient.

For a higher initial pressure, which is provided by a higher tower, the time can be shortened to a period of about 1-60 minutes. A 40-foot tower that gives a pressure difference of roughly about one atmosphere has 30-60 minutes, preferably about

25 40 minutes satisfactory ".

The oxidized mass does not go directly into the tank. Between the mixer and the tank are a heat exchanger 5, an outlet 7 and optionally a pre-pressure chamber 6.

Numerous patents and writings describe various types of mixers.

A special design of an oxygen reactor is disclosed in U.S. Patent No. 3,754,417 to Jamieson, issued April 28, 1973. The reactor has a series of midsoles and the pulp slurry falls from one midsole to another. Oxygen or air is on the midsole 35 and the slurry on the midsole is mixed.

Kirk et al., "Low Consistency Oxygen Delignification in a Pipeline Reactor - Pilot Study", 1977 TAPPI Alkaline 23 74497

The Pulping / Seconadary Fibers Conference, Washington, D.C., November 7-10, 1977, describes a tubular reactor in which pulp is bleached with oxygen at a consistency of 3% using a waterfall system. Oxygen is combined in small increments. In Table 2, 5 piece numbers were measured at 15 minute and 30 minute intervals. Figure 4 is a graphical representation of the decrease in body number versus time. Part numbers were measured at 3, 5, 10, 15, 20, and 30 minutes after oxygen additions.

The following patents are examples of patents that describe various oxygen treatment systems.

U.S. Patent 3,024,158 to Grangaard et al., Issued March 6, 1962, discloses oxygen treatment of pulp to reduce yellowing. Figures 1 and 2 show a two-vessel system in which oxygen is added to a liquid in a second vessel and the pulp is treated with an oxidized liquid in a second vessel.

The reaction time depends on the reaction temperature. The time can be varied between five minutes and three hours at reaction temperatures of 100-160 ° C. Although the method can be used for unbleached sulphate pulp and other pulps with low brightness, it is preferred to use it for bleached pulp. Examples 1-8 of said patent illustrate the treatment of unbleached sulphate pulps. The processing times were 60, 120 and 180 minutes.

The invention also describes two ratios that are important when using oxygen and the parameters of these ratios. The first is the ratio of the oxygen pressure in the atmosphere in contact with the solution to the vapor pressure of the solution at the reaction temperature. It should be at least 0.35 and preferably 0.5 or greater. The second is the ratio of the surface area of the solution in contact with the oxygen-containing atmosphere, in square feet, to the volume of the solution in cubic feet. It must be greater than 4.

Figure 3 of the patent shows an open system in which the pulp 35 is passed through a heat exchanger 23 and then continuously fed through a turbine mixer 24 while supplying oxygen at a pressure of at least 40 psi (2.7579 x 10 Pa). The treated pulp is then fed to a pulp box 22.

The Kamyr buttocks oxygen system is described in U.S. Patent 3,963,561 to Richter, issued June 15, 1976, and Kleppe et al. in the report "Oxygen Alkali Delignification at Kamyr Digester Blow Line Concistency -a status report", 1976 International Pulp Bleaching Conference 2-6 May 1976, TAPPI, November 1976, Vol. 59, 10 No. 11, pages 77-80. In this system, oxygen is added to the pulp in a buffer line between the digester and the oxygen reactor. Oxygen is added just before refining at the bottom of the reactor. The consistency of the pulp is 5-20% and preferably 8-12%. The reactor is of the upstream-downstream type, in which the pulp and oxygen 15 are transported upwards in the conical interior of the reactor and flow downwards in the outer part of the reactor. Oxygen reacts with the pulp in the upstream section of the reactor, where the pulp must linger for 20-30 minutes. During this part of the cycle, the mass is 90% oxidized. In the test bed, the retention time was 20 minutes inside the reactor.

The reactor is associated with a number of mechanical features to prevent the mass from flowing to the top end and to ensure that the mass remains in the conical interior of the reactor for a suitable length of time. The patent relates to the reuse of excess oxygen in a system.

The paper describes the use of the system at Moss's Norwegian plant.

Numerous patents and writings describe the South African Pulp and Paper Industry-L’Aire Liquide-Kamyr-sys-30 themes as it progressed from laboratory to commercial production. Examples are those of Robert et al. U.S. Patent 3,384,533, issued May 21, 1968; and Smith et al. U.S. Patent 3,657,065, issued April 18, 1972.

The pilot plant and commercial unit were described in 35 Myburgh et al. in writing on the 23rd TAPPI Alkaline Pulping Conference. The commercial unit was also described by 25,744 97

Myburgh in a later paper, "Operation of Sappi's Oxygen Bleaching Plant," presented at the 1973 TAPPI Alkaline Pulping Conference.

The 5 oxygen reactors used in the commercial modification of this system are described by Verreyne et al. U.S. Patent 3,660,225, issued May 2, 1972. The reactor is complex and has individual intermediate bottoms for each pulp bed. The consistency of the pulp is 16-67%. In one example, the pulp is given a height of 15 m in the reaction vessel, a reaction time of 30 minutes and a pressure of 150 psig (1.0342 x 10 Pa). The reactor is a large, expensive pressure vessel.

The Billerud system is described in U.S. Patent 4,004,967, issued January 25, 1977. This is also a high-density, high-pressure system.

15 The Toyo Pulp Company system is described in Magano et al. U.S. Patent 4,045,279, issued August 30, 1977 to Nagano et al. in "Hopes Oxygen Pulping Process - Its Basic Concept and Some Aspects of the Reaction of Oxygen Pulping", TAPPI, October 1974. A high pressure vessel 20 is used and the time for the reaction is 15-20 minutes. Figure 5 shows that the reaction rate increases as the consistency increases. Reaction rates for consistencies of 1/10%, 1% and 3% are shown.

The Rauma-Repola system is described in the Federal Republic of Germany's patent publication 24 41 579, March 13, 1975, and Yrjälä 25 et al. in New Aspects in Oxygen Bleaching, dated April 18, 1974. The system uses the Vortex mixer (vortex mixer) shown in Figures 2 and 3 of the patent. By using either multiple passes through a single mixer or multiple mixers in series, it is possible to leach the mass in 5-15 minutes. The consistency is 3%.

Yrjälä et al. "A new Reactor for pulp bleaching" Chemical Industry 29, No. 12: 861-869 (1972) describe a chlorine reactor.

Richter, U.S. Patent 4,093,506, issued June 6, 1978, 35 describes a mixer for mixing bleaching agents such as chlorine or chlorine dioxide with a high density pulp. The rapidly rotating rotor blades mainly fluidize the mass 26 7 4 4 9 7 and the treatment gas is then added to it. Also

The Kamyr reactor is described in an article, "Pilot and Commercial Results of Medium Consistency Chlorination," presented at the Bleaching Seminar of Chlorination 5 and Caustic Extraction, November 10, 1977 in Washington, D.C.

The TAPPI special study "The Bleaching of Pulp" describes and shows on page 325 and 332 the uniaxial and biaxial steam mixers, respectively. The steam mixer 2 has a sweeping area of about 6,500 m per ton of kiln-10 dry pulp.

Several patents and writings describe bleaching kits that use oxygen.

In his undated post, "The Present and Future Role of Oxygen Bleaching," Jamieson presents a series of 15 sets that use oxygen. These include CpOD, COD, OCED, OCDOD, ODEDED, and 0CDEDE.

Rerolle et al. U.S. Patent 3,423,282 describes kits with a central OC kit. These include OCE, OCP and OCH (in situ) * c-va ^ e has been reduced from 15 minutes to 20 minutes and the amount of chlorine has been reduced to 50-70% of the amount normally used.

Smith et al. mention in U.S. Patent 3,725,194 the series ODEDED, SO2-02-SO2-DED, So2-02-H-DED and SO2-O2-DED. Grigorescu "Oxygen Bleaching of Fibrous Pulps", 25 Celluloza Si Hirtie 23 (2), 58-62 (1974) describes the series AODED, COD, CODED and OCDED.

Jamieson et al. “Mill Scale Application of Oxygen

Bleaching in Scandinavia "1973 TAPPI Alkaline Bleaching

The Pulping Conference, 231-238, lists a number of series.

30 These are O, OP, OH. OD, ODED, OCED, OC / DED, CODED, OC / DEHD, OCEDED, OC / DEDED, OHD, OPHD, OHPD, OC / DPD, OC / DEuD and OC.

of

Jamieson et al. "Advance in Oxygen Bleaching" TAPPI, 11/71, 54, No. 11, 1903-1980, compare the OC and CO series.

35 Soteland, "Bleaching of Chemical Pulp With Oxygen and Ozone," Pulp and Paper Magazine of Canada, Vol. 75, No. 4, April 1974, pages 91-96, mentions a series of 74497 27 series comprising oxygen and high-density ozone -kä-treatments of. These include oxygen-ozone, oxygen-ozone-peroxide, oxygen-ozone-hypochlorite, oxygen-ozone-ozone-peroxide, and oxygen-ozone-ozone-hypochlorite.

5 Rothenburg, et al., “Bleaching of Oxygen Pulps with

Ozone ", TAPPI, Vol. 58, No. 8, August 1975, pages 182-185, describe oxygen-ozone, oxygen-ozone-sodium hydroxide-extract-to-ozone, oxygen-ozone-peroxide and oxygen-ozone acetic acid series.Ozone treatment takes place at high consistency-10 sa in all these series.

Kirk et al. "Low Consistency Oxygen Delignification in a Pipeline Reactor - Pilot Study", 1977 TAPPI Alkaline Pulping / Secondary Fibers Conference, Washington, D.C., November 7-10, 1977, describe a tubular reactor in which pulp at 3% consistency is bleached with oxygen using a waterfall system. Oxygen is introduced in small additions. In Table 2, Kap returns were measured every 15 min and 30 min. Figure 4 is a graphical representation of the decrease in body number versus time. Piece numbers were measured at 3, 5, 10, 15, 20, and 30 minutes after hap-20 dripping.

It has been difficult to add oxygen to the pulp at consistencies where it leaves the scrubber. It has also been difficult to be able to mix oxygen in a short time. Most of the previous solutions required either long time periods or a large amount of very large hardware.

Ordinary oxygen systems require multi-million dollar capital investments due to the large vessels used. High-density systems require 30 complex machines to flocculate the pulp prior to hap-treatment. This limits the oxygen treatment to a single step.

It was now decided that it was necessary to shorten the reaction time, provide equipment that does not require a large amount of capital, and operate at the consistencies typically found in pulping and bleaching systems to reduce the power required to operate the system. The pulp is usually removed from the 28 744 9 7 scrubber or subsequent steam mixer at a consistency of about 7-15%. It has the same consistency at other points in the pulp mill. A move was made to try mixing with equipment that is more suitable for a normal pulp mill environment, that could be easily interposed in a pulp mill without major modifications to the equipment in the mill, and that required less power to operate. In doing so, it was thought that the amount of area swept, the area swept by the rotors as the pulp slurry 10 passes through the mixer, is important. This area is defined by the equation: 1440? 6 (r 2-r 2) (R) (N) a = _1 z_ A t 15 where 2 A = swept area per tonne, m / t rj = external radius of the rotor, m * 2 = inner radius of the rotor, m 20 R rotor speed, r / min N = number of rotors t = number of tonnes of mass (calculated as oven dry) passing through the mixer per day.

It was found that the area swept should be 25 10,000 to 1,000,000 m2 / t of oven dry pulp. It was determined that this area had an area of 25,000 to 150,000 m2 / t of oven-dry pulp with certain properties that were better: less power was required, i.e. the reaction kinetics were substantially better. The optimum swept surface area is approx. 65,400 m / t of oven-dry pulp.

It was also determined that oxygen should be introduced into the pulp slurry in the mixing zone. Oxygen should preferably be fed differentially to the pulp as it passes through the mixer. This is done by multiple additions of the chemical through 35 stators that push out the pulp slurry and reduce the rotation of the pulp slurry as it passes through the mixing zone.

29 74497

The rotors, which provide a swept area in the slurry, have front and rear edges with curvature radii of 0.5 to 15 mm. Although the radii of curvature of the leading and trailing edges are usually the same, they need not be. The cross-section of the rotor 5 should preferably be oval in shape, preferably an ellipse with a major axis parallel to the rotational movement. It should also be tapered. The rear edge of the rotor may have a groove and this groove has been treated with a water-repellent coating.

It was also found that the dimension through the central axis of the mixer should be about half of the total internal diameter of the mixer, so that an annular space is formed through which the slurry passes while being processed. A better reaction occurs when the shaft diameter is at least half the inside diameter of the mixer than when the shaft diameter is smaller.

The mixer should have a mixing zone with 2 swept areas of 10,000 to 1,000,000 m / t of oven dry pulp. The preferred area is 25,000 to 150,000 m2 and the optimum area 2 to 20 is about 65,400 m. The rotors in the mixer preferably have front and rear edges, each with a curvature of 0.5 to 15 mm, and having an elliptical cross-section. Oxygen is fed to the mixing zone through stators.

25 The inventors decided to study both the high cost and the long-term need for oxygen bleaching. It was decided to add oxygen to the existing system and determine the results. Contrary to previous teachings in the art, it was found that oxygen can be added to the pulp and handled at a consistency where the pulp normally comes from the scrubber or subsequent steam mixer, that much processing takes less than a minute in the mixer and no long reaction or capital intensive equipment is required. All that is needed is a relatively small mixing device that thoroughly mixes the mass and gas.

30 744 97

Oxygen can be added to the extraction step, between scrubbers, between the scrubber and the subsequent storage tank, or in the butt digester butt after the pulp has been washed in the digester. Alkali, steam and oxygen are added to the butt and the oxygen is treated with pulp. The dozer line transports the pulp to either a storage tank, a diffuser or other handling. These are not an important part of oxygen treatment.

Several desired processing sets are possible. These include O-X-O and 0-O-X-0, where X is chlorine, chlorine dioxide-10 di, a combination of chlorine and chlorine dioxide, hypochlorite, peroxide or ozone. This series may be followed by a D-phase.

Although the mixer was originally designed to overcome the problem of mass oxidation, it is also useful for non-condensable gases such as ozone, air, chlorine, chlorine dioxide, sulfur dioxide, ammonia, nitrogen. carbon dioxide, hydrogen chloride, nitric oxide and nitrogen peroxide. These gases can also be described as unsaturated in that they do not condense into liquids but heat up even after contact with the mass. The mixer can also be used to mix highly superheated steam with the pulp.

The invention relates to a method for mixing a chemical with a wood pulp having a consistency of 7 to 15%, wherein the chemical is an uncondensed gas, an unsaturated gas or a strongly superheated steam, and wherein the chemical is introduced into the pulp in the mixing zone. The method is characterized in that the mixing zone has a series of rotating members passing through the pulp, having a main axis extending in the direction of rotational movement and front and rear edges, the rotating members passing through the pulp transversely to the pulp flow direction and sweeping area 2 through the pulp. is 10,000 to 1,000,000 m / t of oven-dry mass, and wherein the radius of curvature of the leading edge is 0.5 to 15 mm.

The invention also relates to a mixer for use in the method 35 described above, comprising a housing having an inlet and an outlet, a shaft and a mixing zone. The agitator is characterized in that the shaft 560 has a plurality of rotors 570 in the mixing zone having leading and trailing edges 572, 573, the leading edge 572 having a radius of curvature of 0.5 to 15 mm, 40 and the rotors 570 rotatable through the slurry 3i 74497 across the slurry. and have a sweep area of 10,000 to 1,000,000 m / t of dry solids in the slurry.

The figures in the appendix show the following: Figure 1 (A-C) is a diagram of a prior art pulping and bleaching process.

Figure 2 is a diagram of the oxygen system shown herein used in a dozer line in connection with a refiner.

Figure 3 is an oxygen diffuser used with the refiner 10 to add oxygen to the refiner.

Figures 4 and 5 are cross-sections of grinding with the diffuser of Figure 3.

Figure 6 is a diagram of a modified system used in a dozer line.

Figure 7 is a diagram of prior art oxygen bleaching systems.

Figure 8 is a diagram of the oxygen bleaching system disclosed herein.

Figure 9 is a diagram of the oxygen system 20 shown here in the extraction step.

Figure 10 is a diagram of the oxygen system shown herein between scrubbers.

Figure 11 is a diagram of the oxygen system shown herein between the scrubber and the storage tank.

Fig. 12 (A-C) is a diagram of a pulping and bleaching process using the oxygen bleaching systems of Figs. 8 and 9 and a modification of Fig. 11.

Fig. 13 (A-C) is a diagram of a pulping and bleaching process using the oxygen bleaching system 30 of Fig. 11 and the modification of Fig. 11.

Figure 14 is another diagram of a prior art bleaching system.

Figure 15 is a diagram of a pulping and bleaching process using the systems of the present invention.

Figure 16 is an isometric view of a mixer that may be used in the present invention.

Fig. 17 is a side plan view of the mixer shown in Fig. 16.

Fig. 18 is a cross-sectional view of the mixer taken along line 18-18 of Fig. 1740.

32 74497

Fig. 19 is a cross-sectional view of the mixer taken along line 19-19 of Fig. 18.

Figure 20 is a plan view of the rotor.

Fig. 21 is a cross-sectional view of the rotor taken along line 21-21 of Fig. 20.

Figure 22 is a plan view, partially in cross-section, of the modified rotor.

Fig. 23 is a cross-sectional view of the modified rotor taken along line 23-23 of Fig. 22.

Fig. 24 is a plan view, partially in cross-section, of a stator used in a mixer.

Fig. 25 is a side plan view, partially in cross-section, of the modified stator along a line corresponding to line 25-25 of Fig. 24.

Fig. 26 is a cross-sectional view of the stator taken along line 26-26 of Fig. 24.

Fig. 27 is a cross-sectional view of the valve taken along line 27-27 of Fig. 25.

Figure 28 is an isometric view of the modified mixer.

Fig. 29 is a side plan view of the mixer of Fig. 28.

Fig. 30 is a cross-sectional view of the mixer taken along line 30-30 of Fig. 29.

Fig. 31 is a cross-sectional view of the mixer taken along line 31-31 of Fig. 30.

Figure 32 is a cross-sectional view of the rotor used in the reactor of Figures 28-31.

Fig. 33 is a cross-sectional view of the rotor taken along line 33-33 of Fig. 32.

Fig. 34 is a graph comparing two mixers.

Figure 35 is a cross-sectional view of the modified mixer.

Fig. 36 is a cross-sectional view of the modified mixer taken along line 36-36 of Fig. 35.

Fig. 37 is an enlarged cross-section of the interior of the mixer shown in Fig. 35.

Figures 2-5 show the present invention fitted to a butt wire with a grinder. Figure 2 is a diagram of the process and Figures 3-5 are proposed modifications to the refiner to add oxygen to the pulp slurry closer to the actual refining mechanism.

The system shown in Figure 2 should be compared to the butt-lead-oxygen system described in the Kamyr patent and the aforementioned paper. It should be remembered that the 5 Kamyr system required a special upstream-downstream tower refiner to provide a retention time of at least 20 minutes after treating the pulp with oxygen.

In contrast, in this system, it is only necessary to add oxygen, alkali, and heat prior to grinding in the butt-mill grinding system of a conventional canister. In a system with two refiners, the latter refiner is preferred because it has more individual fibers at this stage. This is the system shown in Figure 2.

In this figure, the reference numerals are the same as those shown in Fig. 15a, with 10 'being the incoming chips, 11' being the process water, 12 'being the steam, 13' being the pulping chemicals and 14 'being the casserole. Again, the chips 10 'may be treated prior to entering the digester 14' by pre-steaming or impregnating with cooking chemicals or some other treatment. Again, any pulping method can be used and the pulping conditions for any particular method depend on the type of wood chips and the desired product. Pulping conditions and amounts of chemicals are well known.

The digester 14 'should be continuous, as most of the delignification products should be removed before oxygen treatment. Otherwise, too much oxygen is used in the reaction with the delignification products and not with the pulp fibers. The washing step of the bed performs this washing. Reference numerals 30 15 'and 16' denote, respectively, the washing water entering the washing stage of the bed and the discharge stream leaving it.

As in Fig. 1, reference numerals 17 ', 20' and 21 'are three parts of a dozer line, 18' and 19 'are two grinders, 22' 35 is a storage tank or diffuser and tank, and 23 'and 24' are pump and line carrying pulp from the tank. 22 'for further consideration.

It is an object of the present invention to treat the washed pulp with oxygen with as few changes in equipment as possible. Sodium hydroxide and steam are added to the pulp slurry in line 20 'between refiners 18' and 19 '. Sodium hydroxide, which both adjusts the pH of the pulp and buffers the oxygen reaction, is added from line 25. Other suitable alkalis, such as white liquor, may also be used. Steam is added through line 5 26. The steam raises the temperature of the pulp to a temperature suitable for oxygen treatment. Oxygen is added through the pulp line 27. In a system with two grinders, the addition of chemicals and steam before the second refiner is advantageous because there are 10 more individual fibers in the second grinding step.

The wires used to transport these various chemicals to the process are shown at the top of Figure 2. Line 360 'supplies process water to lines 11' and 15 '. Line 362 'carries sodium hydroxide to line 25. Line 364' introduces steam to lines 12 'and 26. Line 366 supplies oxygen to line 27.

In some cases, the base is used both as a cooking chemical and for oxygen treatment, such as in a soda process where sodium hydroxide is used for both cooking and oxygen treatment or in a sulfate process where white liquor 20 is used for both cooking and oxygen treatment. In this case, line 362 'would also feed line 13'.

The amount of oxygen used depends on the yield and the K or piece number of the mass to be treated and the desired result of the treatment. Oxygen treatment requires 5-50 kg oxygen / t 25 oven-dried unbleached wood pulp.

In low yield, low kappa number pulp, the purpose of oxygen treatment would normally be bleaching. The actual yield and number of pieces would depend on the pulping method used, but these pulps are used for bleached products. The number of chunks and brown pulp for pulp used in bleached products is usually about 30 to about 40. The amount of oxygen used to bleach the pulp would be 5-40 kg / t of oven-dry pulp.

In high-yield, high-density pulp, which is a type commonly used for linerboard, the purpose of hap-treatment is to improve certain properties of the product. The number of pieces of dozer wire and brown mass for this mass is usually about 80-120. This allows the mill to either increase certain property values of the product with the same mas-40 yield or maintain the property value while increasing the yield 35 7 4 4 9 7. For example, the use of 12-50 kg of oxygen for high yield, high bulk density pulp either increases the ring slip strength of the pulp liner or keeps the ring slip strength at the same value and increases the yield. The ring slip density is determined by the method TAPPI Standard T 818 OC-76.

Other conditions may require adjustment for oxygen treatment. The pH for any oxygen treatment in any environment should be between 8-14. In this environment, the amount of alkali, expressed as sodium hydroxide, required to reach this pH is between 0.25 and 8% of the oven dry weight of the unbleached wood pulp. The temperature for some oxygen treatment in any environment is usually between about 65 and about 121 ° C. Typical oxygen phase temperatures are from about 82 to about 99 ° C. However, the actual temperature at one oxygen stage depends on the ability to heat the pulp so that it can range from about 65 ° C to about 121 ° C depending on the placement of the oxygen stage in the system. The pulp from the digester may be at the temperature required for the oxygen reaction. If not, the mass is heated to either set or maintain it at the temperature required for the oxygen reaction during the mixing step.

Figure 2 shows the sampling points marked A, B and C. A is in the butt wire 17 'after the baffle 14' 25; B is in the butt line 21 'after the refiner 19'; and C is at the outlet of the storage tank 22 '. These are the three points where samples were taken and tested in a factory test of this system.

The pulp left the belt digester at 14 '71 ° C and a pressure of 1380 30 kPa. Its pH was 10.5. The amount of unbleached pulp passing through the system from the digester throughout the test was 14.3 t of oven-dry pulp per hour. The pulp passed through the grinder 19 'in about 1.5 seconds and remained in the storage tank 22' for about 50 minutes. The storage tank 22 '35 was open to the atmosphere and the slurry ran from the butt pipe 21 to the open tank.

The system was first tested for about six hours to determine the amount of residual lignin in the unbleached pulp at point A and point C to determine if there were any bleaching effects in the standard system.

30 74497 Samples were taken at points A and C at the time intervals shown in Table I, and the number of pieces in each sample was determined. The accuracy of the measurements of these individual samples was checked during the test by taking a set of samples, calculating the average of the number of pieces of these 5 samples and comparing this average with the number of pieces of the individual sample. These average kappa numbers A Avg and C Avg in Table I and the kappa numbers of the individual sample are within experimental accuracy.

10 The different kappa numbers for the unbleached pulp samples are shown in Table I.

Table I

Time Number AC Difference A Avg C Avg 15 0:01 28.0 0:35 35.4 1:00 33.2 1:30 31.2 2:00 32.4 20 2:30 31.9 3:00 32 .0 32.5 3:30 29.9 32.7 4:00 37.6 4:30 38.7 25 5:00 36.4 5: 30_36.8_37.8

Mean 33.3 34.0 +0.7 From these results, it can be seen that no bleaching occurred between the sample point A, the outlet 30 of the flux 14 'and the sample point C, the outlet of the storage tank 22'.

A 6-hour oxygen-free control test was followed by a 5.25-hour oxygen test. The pH was between 7 and 14 and the temperature between about 65 and about 121 ° C.

During this test, the amount of oxygen added to the pulp Mi-35 was measured approx. every half hour and recorded as pounds of oxygen added per hour. This has been converted to kilograms. Since the flow of unbleached pulp was essentially constant, 14.3 t kiln-dry pulp / h, it was possible to determine the added amount of oxygen in kilograms 40 oxygen per tonne of kiln-dry unbleached wood pulp.

37 74497 During this test, the oxygen flow ranged from a low amount of 6.7 kg / t kiln-dry unbleached pulp to a high value of 40 kg / t kiln-dry unbleached pulp. The average amount of oxygen was 15 kg / t of oven-dried unbleached 5 pulp. Sodium hydroxide was added in an amount of 64 kg / t oven-dry unbleached pulp and steam was added in an amount of 612 kg / t oven-dry unbleached pulp. The pulp entered the second refiner 19 'at a temperature of 70-97 ° C, a pressure of 621 kPa and a pH of 12.5.

10 Again, pulp samples were taken at points A and C at the time intervals shown in Table II, and the mass numbers of the pulp sample were measured. This was done to determine if oxygen bleached the pulp. These chapters are given in columns A and C of Table II . The number of pieces at point C was, on average, 7.5 to 15 points lower than the number of pieces at point A during oxygen treatment, indicating that bleaching had taken place.

A second set of tests was performed to determine where bleaching occurred in the system.

In the first part of these tests, again 20 samples were taken at points A and C to see if there was a correlation between these tests and other N 2 -C 2 bleaching tests performed simultaneously. The results of these correlation tests are given in columns A2 and · of Table II.

The second part of the tests was performed during the A2-C2 ~ tests. Samples were also taken at A and B and the kappa numbers were determined. The samples at point B were taken at approximately the same time as the samples at point A because the mass is in the grinder 19 'for about 1.5-2 seconds. The maximum time in the refiner would be 10 seconds. The results of these are shown in columns A2 and B of Table II. From these tests, it can be seen that the kappa number drop through the refiner 19 'was 7.5, essentially 35 ti between the full kappa number drop points A and C. These tests show, with experimental accuracy, that the reduction in the total number of pieces, i.e. the removal of lignin, takes place in 38 74497 mills between points A and B. The first chapter number in B, 28.5, is the same as the corresponding number in C2 and the second chapter number B, 31.4, is almost the same as the corresponding number in C2, 31.5. Thus, these tests have shown that val-5 leaching occurs in the refiner 19 between the oxygen addition point and point B.

39 7 4 4 9 7

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The brightness of the samples taken at points A and C was also checked. The average brightness of the A2 pulp samples was 18.9 and that of the C2 pulp samples was 22.3.

Numerous other measurements were made during the oxygen tests. Headline fringes, unbreakable fiber bundles, were measured at points A and C. The average headland content was 2.2% of the oven dry weight of the pulp at point A and 0.67% of the oven dry weight of the pulp at point C. The dry matter content of the filtrate in the butt pipe material was 3.6% by weight of the oven dry pulp.

The physical properties of the pulp were also tested.

These properties were permeability, puncture, tear, folding, breaking length, density, and viscosity.

The results of these tests are shown in Table III. 15 Numerical values are given in three sets. The first set is the average of all bleached pulps tested. The second set is for a specific mass sample. The third set is for comparison and is the average of tests on unbleached pulps prepared with equipment before and after 20 bleaching tests.

41 74497

Table III

Physical test Test mass Test mass Reference

Mean Sample mass

Initial CSF 703 708 715 5 Time to 550 CSF 30 min 29 min 34 min

Time to 400 CSF 49 min 50 min 53 min

Time to 250 CSF 67 min 68 min 70 min

Outbreak Initially 14.3 12.1 12.8

Outbreak (? 550 CSF 64, 4 62.1 67.1 10 Outbreak (§ 400 CSF 72.7 69.7 72.4

Burst @ 250 CSF 75.6 73.1 74.3

Tearing Initially 229 206 225

Tear 550 CSF 176 179 159

Tear 400 CSF 160 157 151 15 Tear 250 CSF 151 149 147

Layout Initially 7 11 5

Layout <9,550 CSF 610,705,545

Folding (§ 400 CSF 1045 1045 660

Folding (? 250 CSF 1570 1365 810 20 Breaking length Initially 1700 m 2700 m 2700 m

Breaking length® 550 CSF 7700 m 7300 m 8000 m

Breaking length® 400 CSF 8700 m 7800 m 8500 m

Breaking length® 250 CSF 9000 m 8200 m 8900 m

Density Initially 0.49 0.49 0.47 25 Density @ 550 CSF 0.58 0.58 0.58

Density @ 400 CSF 0.61 0.62 0.62

Density® 250 CSF 0.62 0.63 0.62

Viscosity 75 76 61 During this test, it was important that the device for adding oxygen, 30 steam and sodium hydroxide was of the simplest possible type. In all cases, the chemicals were added through tubes that inserted into the butt pipe 20 '. The wires were upstream of the grinder 19 '.

To determine the ability of oxygen to alter the properties of the pulp, pulp having a kappa number of 120 and a yield of 58.6 was treated with oxygen in a pilot plant equipment. Oxygen was fed to the pulp in an amount corresponding to 20 kg per ton of kiln dry 42 7 4 4 9 7 pulp. The temperature was 90 ° C. The addition of sodium hydrochloride was 4% by weight of the oven-dry mass. No preservative such as magnesium oxide was added. In fact, no preservative was used in any of the 5 experiments described in this patent application.

The treated pulp had a kappa number of about 65. It was compared to a sulphate pulp with a kappa number of 58. The tests were performed with a permeability number of 675 Canadian Standard Freeness. The ring-treated strength of the oxygen-treated pulp was 15% higher than that of the sulphate pulp and the puncture was 2% higher than that of the sulphate pulp.

Again, the actual chemical feed depends on the starting mass and whether you want to increase the properties or the yield. The oxygen supply can be 12-50 kg / t of oven-dry pulp.

The alkali addition, expressed as sodium hydroxide, would normally be 3.6 to 4.9% and the temperature would normally be 92 to 95 ° C. A small amount of preservative could be used. This amount would not exceed 0.5%, calculated on the weight of the oven-dry mass.

The number of pieces of the final product would be between 65-69; 20 ring slip strength, relative to sulphate mass, less than 3% as yield is increased, 2% higher if better properties are desired; and the puncture, relative to the sulphate mass, is the same in numerical value if the yield is increased, up to 6% if better properties are desired.

25 Much of the handling would take place in the mixer and the bulk in the mixer and on its way to the non-return valve or to the top of the pipe in the mixer outlet line.

Figures 3, 4 and 5 show a unit that would distribute oxygen more evenly. Figure 3 shows the distribution unit as such and Figures 4 and 5 show cross-sections of grinding containing the unit.

The unit 370 comprises an inlet pipe 371 which fits into the inlet of the refiner housing and is fixed in place by bolts passing through holes 372 in the flange 35 373.

A plurality of L-shaped tube diffusers 374 are evenly spaced and oriented axially around the tube and flange «74497. Each diffuser has an inlet section 375 and an outlet section 376. The inlet section 375 extends radially along the flange 373 and the outlet section 376 extends longitudinally of the tube 371. The tube can have any 5 cross sections. There are several ways to attach the diffusers 374 to the pipe and flange. The inlet compartment 375 may extend along the inner or outer surface of the flange 373, be attached to cavities on the inner or outer surface of the flange 373, or may be in and formed by the walls of the flange. In the latter structure, the outlet pipe would run radially from the flange 373, as shown in Figure 2. Similarly, the outlet compartment 376 could be attached to the inner or outer wall of the tube 371, fitted into cavities in the inner or outer walls of the tube, or be inside and formed by the walls of the tube. 15 They would be formed into or from walls by casting when the pipe and flange are formed or drilled through the wall. The preferred shape is shown in Figure 3. The inlet compartment 375 is formed on the flange and the outlet compartment 376 is attached to the inner wall of the pipe. The diffuser has one or more out-20 inlets for oxygen. Six diffusers would disperse enough oxygen into the mass.

Figure 4 shows the unit in connection with the refiner. The figure shows a simple disc grinder. Only the main parts of the refiner are marked with reference numbers.

The refiner 380 has an inlet 381, a screw conveyor compartment 382, a refiner compartment 383 and an outlet 384. The refiner shaft 385 is inside the housing. Attached to the shaft is a screw conveyor 386 and a rotating refining member 387. A rotating refining plate 388 is attached to the member 387. A fixed refining member 390 and a fixed refining plate 391 aligned with the rotating plate 388 are attached to the refining housing 389. The shaft 385, the conveyor 386, the rotating grinding member 387 and the plate 388 are rotated by a suitable motor 392.

In this refiner, the unit 370 would be part of the conveyor wear plate. The diffusers 374 would be either embedded in the tube 371 or formed in the tube, as described above. This would allow oxygen to be fed after the conveyor part.

44 7 4 4 9 7

Oxygen is supplied to the diffusers through an oxygen manifold 394. Oxygen enters the diffusers 374 through the manifold 394 and is added to the pulp after the conveyor 386. The oxidized pulp exits the refiner through outlet 384.

The dozer line 20 'is attached to the inlet 381.

Figure 5 shows the use of unit 370 in a refiner without a conveyor compartment. The reference numbers are the same as in Figure 3.

Each type of grinder has a relative rotational motion between opposing surfaces that are spaced apart to allow material to flow between them. Plate grinders are normally used due to the fact that the free spacing and compression of the plates can be changed, depending on the mixture ratio of the refiner feed and the desired end product. There are other types of grinders that can be used. In a standard twin-disc grinder, the rotating disc has grinding plates on each side that act against the plates fixed opposite. In another type of double disc mill, both mill plates 20 are mounted on discs that rotate in opposite directions to provide both a rotating and abrasive effect. The discs are mounted on different shafts, which can be concentric. A conical grinder can also be used.

In some plants, there is no refiner in the dozer line between the canister 25 14 and the buffer tank 22. It is now possible to achieve good treatment by adding alkali, steam and oxygen lines to the butt line and a mixer such as a mixer 116. This is shown in Figure 6. The other reference numerals are the same as in Figure 2.

The mixer 116 may be a refiner, such as the refiner shown in Figures 4 or 5. For example, the grinder, when stopped, can be used as a mixing device. The free space between the discs has been tested at approx. 13 mm and can be up to 75 mm. Thus, the clearance can be from a few millimeters to n.

35 to 75 mm. This narrow passage causes the pulp slurry and oxygen to mix. Another suitable mixer would be a mixer that is relatively small and thoroughly mixes 45 7 4 4 9 7 mass and gas. Several suitable mixers are described later in this patent application.

The mass in the mixer or grinder should be subjected to back pressure. This is achieved by an upflow line 5a after the mixer, which pipe generates hydrostatic pressure with the mixer. A pressure valve is preferred. The valve may be connected to an upstream pipe. The valve may be located in the butt line 21 'downstream of the refiner 19' or in the line 21 "downstream of the mixer 116. The valve 10 may be located either immediately after the mixer or refiner or at the upper end of the line before exit.

The maximum pressure in the mixer does not normally exceed 830 kPa and at the upper end of the line it does not normally exceed 345 kPa.

Figures 7 and 8 compare a prior art oxygen-15 leaching system of the type disclosed by Verreyne et al. U.S. Patent No. 3,660,225, the size and complexity of the system of the present invention. Both drawings are on the same scale. Each unit would process the same amount of mass calculated as oven dry.

In the prior art system shown in Figure 7, the pulp 400 is conveyed from the plant 401 by a pump 402 to a storage tank 403. In a storage tank 403, the pulp is mixed with an alkali solution 404 from a filtrate storage tank 405. At this point, a preservative would also be added to the pulp. The treated mas-25 mixture 406 is transferred by a pump 407 to a dewatering press 408, which removes enough water from the pulp to increase the consistency of the pulp slurry to about 20-30%. This material is then conveyed by a pump 409 to the top of the oxygen reactor. Pump 409 comprises a series of screw conveyors, which is the only way 30 to pressurize a mass having such consistency. The upper end of the reactor 410 has a effervescent 411 which distributes the pulp evenly to the upper plane 412 of the reactor. The pulp passes down through the other planes 413-416 and is treated with oxygen as it passes through the planes. Based on the levels, the bleached pulp 35 417 is transported to the storage tank 418.

This plant should be compared to the system of the present invention shown in Figure 8. The mixing tank 403, the filtration storage tank 405, the press 408, the pump 409 and the reactor 410 have been replaced by a simple mixer 420 in which oxygen is mixed with the pulp 400 '.

By way of comparison, the system of Figure 7 requires six times as much energy as the mixer or system of Figure 8. For the same amount of mass, the system of Figure 7 would require 2,238 kW of group motors to operate the reactor and the various equipment components associated with the reactor, while the agitator of Figure 8 would require a 373 kW motor.

The mixer of Figure 8 is also capable of operating at the consistencies commonly found in pulping and bleaching systems. This would generally be the consistency of the pulp as it leaves the scrubber or subsequent steam mixer, a consistency of about 8-15% from the scrubber and about 1% lower for the steam mixer.

Figure 9 shows an oxygen mixer in the normal basic extraction step of a bleaching system. It shows that a small change can turn the basic extraction step into an oxygen treatment step. To compare the extraction step in the extraction step in Fig. 1, the same reference numerals have been used. The operation of the various parts of the apparatus 20 - scrubbers 201 'and 221', steam mixer 206 ', extraction tower 213' and sealing tanks 293 'and 313' is the same as in the prior art extraction step in Figure 1.

The mass and wash water flows through the system are also the same as in Figure 1.

The pulp 195 'enters the scrubber 201' where it is washed, dewatered and treated with a base, usually sodium hydroxide. The consistency of the pulp leaving the scrubber is usually between 8-15%. The effluent 203 'is then mixed with the base and steam in a steam mixer 206'. The consistency of the pulp decreases in a nl 1% steam mixer. From the steam mixer, the pulp passes to the extraction tower 213 ', where it remains for a normal period of time. It is diluted and transported to a scrubber 221 'where it is washed and dewatered.

Although the washer 221 'may be a diffuser, it is shown and described as a vacuum or pressure drum washer.

47 74497

In scrubber 221 'the water is either fresh process water from line 310', from the countercurrent filtrate from line 343 'or a combination thereof, and in scrubber 201' the wash water is either fresh process water from line 290 'or from the countercurrent filtrate from line 5,323' or a combination thereof.

The filtrate from scrubber 201 'is stored in a sealing tank 293' and used as dilution water via lines 295 ', 297' and 301 ', as wash water via line 303' or taken to drain-flow treatment via line 294 '. It is shown to be treated separately from the effluent in line 350 ', because the effluent, if it is from the chlorine stage, would be treated separately from the effluent from the oxygen stage.

Similarly, the filtrate from scrubber 2211 is stored in a sealed tank 313 'and used as dilution water through lines 1555, 317' and 321 ', as wash water via line 323', or treated as an effluent through line 314 '. Because the oxygen effluent has little, if any, chlorine components, it can be combined with the effluent from the brown pulp scrubbers and digester and treated in a recovery furnace, thereby reducing the amount of material that must be discharged into a nearby body of water or water body.

The supply lines are 360 '"for process water, 362'" for sodium hydroxide solution and 364 '"for steam.

The description of the step is thus, except for the splitting of the effluent-25, similar to the description of the extraction step in Figure 1. Only a small change is needed to convert this extraction step to an oxygen step. This is the addition of oxygen mixer 211 to line 209 ', the addition of oxygen line 212 to either mixer 211 or line 209Ά just in front of mixer 30 and the addition of oxygen supply line 366 ". The pulp exits steam mixer 206' through line 209Ά and enters oxygen mixer 211 and oxidized mass exits 209'B and enters the extraction tower 213 'The amount of oxygen fed to the pulp would be 11-28 kg / ton of oven dry pulp 35 The preferred range is 17-22 kg of oxygen / ton of kiln dry pulp.

All conditions — time, temperature, pressure, consistency, pH, and chemical addition — can remain approximately the same 48 7 4 4 9 7 as they were in the extraction step shown in Figure 1. The temperature would normally be raised from 71-77 ° C to the extraction step to 82-88 ° C for the oxygen treatment step, as the treatment improves at higher temperatures. Again, the temperature can be as high as 121 ° C. The amount of time, expressed as sodium hydroxide, is 0.5 to 7% by weight of the oven-dry mass. Oxygen channeling after mixing is of little importance. If the extraction tower is a tower with a downward flow, it remains a downflow tower. The sical location of the mixer 211 fy-10 is a matter of sole criticism for its convenience, simplicity of installation and maintenance. If it can be placed on an existing wire, it will be placed. If comfort requires that it be placed on the floor of the bleaching plant, it is placed on the floor of the bleaching plant and an external line can carry the pulp slurry to the upper end of the extraction tower 213 '.

Mixing provides thorough contact between the gas and the slurry and appears to divide the gas into very small bubbles. However, some 20 larger bubbles and gas pockets may occur. The presence of large gas bubbles and gas pockets up to the size of the pipe through which the pulp slurry passed has been observed. These have not affected pulp quality or pulp handling.

The mass in the mixer should have a back pressure. This is achieved by an upflow line after the mixer, which generates hydrostatic pressure with the mixer. A pressure valve is preferred. The valve may be connected to an upstream line. The valve may be located in line 209'B downstream of mixer 211. The valve may be either 30 directly behind the mixer or at the top of the line prior to exit.

The maximum pressure in the mixer would not normally exceed 830 kPa and at the upper end of the pipe it would not normally exceed 345 kPa.

35 In the factory test of the system, samples were taken in D, E and F. At point E, the sample was taken at the upper end of the tower 213 'and not directly after the mixer 211 because it was impossible to take the sample after the mixer. It took about a minute for the slurry to reach point E from the mixer. In these experiments, the mixer was on the floor of the bleaching plant and an external wire carried the sludge to the top of the tower.

5 Table IV

PBC

D E F

1.4 1.13 0.95 1.4 1.13 0.90 10 Figure 10 shows an oxygen mixer between two scrubbers. In this case, the scrubbers are brown pulp scrubbers. The reference numerals are again the same as in Figure 1 and the conditions in these two washers are the same as those shown in Figure 1.

The differences between this unit and the unit of Figure 1 are the addition of a steam mixer 86, a pump 76, a mixer 88 and lines 85, 87 and 89. Line 85 adds alkali to the mat 73Ά as it exits the scrubber 71 '. The amount of alkali fed to the mat, expressed as sodium hydroxide, is between 0.1 and 20% by weight, preferably between 2 and 4%, based on the oven-dry weight of the pulp. The treated mat 73Ά is then passed to a steam mixer 86 where it is mixed with alkali and steam from line 87 to raise the temperature of the pulp to 65-88 ° C and possibly as high as 121 ° C. From the steam-25 mixer 86, the pulp slurry 73'B is conveyed by a pump 76 to the mixer 88, where it mixes with oxygen from line 89. The amount of oxygen added depends on the K-number of the pulp and the desired result. The reasons for adding oxygen in brown pulp scrubbers are the same as adding it to the butt-30 line and using the words amounts. This is normally 5-50 kg / ton of oven-dry pulp. The two standard ranges for bleaching in a brown pulp system are 22-28 and 8-17 kg oxygen / ton oven-dried pulp. The latter is a preferred area. The oxidized pulp 73'C then passes to the vat 90 'of scrubber 91' 35.

The scrubber after the mixer can be a diffuser.

so 744 97 Again, the mixer should have a back pressure. This pressure is provided in the same manner as the pressure is applied to the mixer 211, by an upflow line, a pressure valve, or a combination thereof. The position of the valve and the maximum pressure are the same as with the mixer 211.

Figure 11 shows a system located in a scrubber, such as a brown pulp scrubber 91 ", and a storage tank, such as a storage tank 110 '. Reference numerals are again the same as those used in Figure 1. The changes are steam mixer 106, mixer 108, alkali line 105 and its supply. addition of line 362 '"", steam line 107 and its supply line 364 ,,, M and oxygen line 109 and its supply line 366 "". Amount of alkali and oxygen added to the pulp, temperature and time of pulp between alkali addition and oxygen addition and pressure in se-15 mixer and in the outlet line, and the methods for generating these pressures are the same as in the system of Figure 10. Other operating conditions remain the same as in Figure 1.

In each of these systems, the time between alkali addition and oxygen addition is usually 1 to 5 minutes.

20 The exact time depends on the placement of the equipment and the speed of the pulp.

A factory test was performed using the system shown in Figure 11. In this system, agitator 108 was mounted on the floor and pipe 93 "C transported slurry from agitator 108 25 to the upper end of tower 110 '. The tower was open to the atmosphere. A partially closed valve near the outlet end of pipe 93" C provided a back pressure of 275 kPa. The hydrostatic pressure in the line was 241.5 kPa, so that the pressure inside the mixer was 517.5 kPa.

30 Four test runs were performed under slightly different conditions to determine both the total lignin removal efficiency of the system and the percentage of lignin removal in each part of the system. K-number measurements were made before and after the mixer 108, the outlet of line 93 "C, the outlet of the tank 110 'and the outlet of the thickener 121' (Figure 7b) downstream of the tank 110 '.

51 74497

In a comparative experiment in which no oxygen was added to the system, it was determined that the K-number decreased by one reading unit between the inlet of the mixer 108 and the outlet of the thickener 212 '. This was probably due to the sieve effect. In the total calculation of Lig-5 soybean removal, the figures were corrected for this 1 K drop.

The various K-numbers were taken within the system to determine the percentage of total identification or decrease in K-number that occurs as the pulp passes through mixer 108, line 93 "C, tank 110 '10, and thickener 121'. Wash jets were added to these thickener tests. the passage through mixer 108 took 10-15 seconds, through line 93 ° C 2.5 to 3.5 minutes, and 0.5 to 3 hours through tank 110 'or thickener 121'. It was determined that in these tests, 30% of the total lignin removal occurred in mixer 108, 40% occurred in line 93 ° C, 8% occurred in tank 110 ', and 21% occurred between tank and thickener. The latter decrease is due to pulp sieving.

The actual conditions in the mixer are given in Table-V to V: temperature in degrees C; kg of base, expressed as sodium hydroxide and oxygen per tonne of oven-dry mass; pressure measured in kilopascals; K-numbers at various points within the system; and the percentage reduction in the K number. In the experiment, about 1 percent reduction in the thickener outlet in the last 25 pipelines is a decrease between the line end and the thickener outlet.

52 74497

Table V

Experiments 12 3 4

Mixer conditions 5 Temperature, ° C 79.5 82 93 88

Base, kg / t oven - dry mass

Oxygen, kg / t oven - dry mass 22.7 25.2 20.2 25.2

Pressure, kPa 517.5 517.5 517.5 517.5

Total lignin removal 10 Before the mixer K-number 19.6 25.4 19.9 24.1

Corrected K-number 18.6 24.4 18.9 23.1

After thickener K-number 15.6 19.2 15.1 17.8 15% decrease in K-number 16 21 20 23

Delignification inside the system at the agitator's inlet K-number 19.6 25.4 19.9 24.1

At the mixer outlet 20 K-number 18.5 23.3 18.6 21.3% of the total reduction 25 34 27 29

At the top of the line K-number 16.8 21.5 16.0 19.8% of the total reduction 44 29 54 40 25 At the outlet of the tank K-number - 20.5 16.0 19.3% of the total reduction 16 0 8

At the thickener outlet, a K-number of 15.6 19.2 15.1 17.8 30% of the total reduction 31 21 19 23 These numerical values indicate that in each system described in this application, a valve should be placed in the line downstream of the oxygen mixer to counterbalance the mixer. They also show that much of the lignin-35 removal takes place in less than a minute in a mixer. It can happen in 10-15 seconds or less.

53 7 4 4 9 7

Most take place within minutes of the mixer and outlet line immediately after the mixer.

The maximum pressure in the mixer would not normally exceed 830 kPa and the pressure at the upper end of the line, if a hydrostatic branch is used, would not normally exceed 345 kPa.

The mixer has also been used under hydrostatic pressure alone.

The oxygen systems of Figures 9, 10 and 11 are shown in the bleaching system of Figure 12. Figure 12 shows the same size-10 female system as Figure 1 and the same reference numerals are used throughout these figures. The system shown in Figure 1 comprises pulping the chips in either a batch or flux digester, washing the pulp after cooking, sorting, dewatering in a thickener 121 and a DcEDED bleaching kit. Figure 12 shows pulping, post-cooking pulp washing, sorting and OOCOD bleaching kit. For most, the operating conditions — time, temperature, pH, consistency, and chemical addition — are the same in Figure 12 as they were in Figure 1.

The differences between the system shown in Figure 12 and the system shown in Figure 1 are indicated by brackets at the bottom of Figure 12.

The first difference between the process shown in Figure 12 and the process shown in Figure 1 is indicated by a waveguide 430. This is the scrubber-oxygen system of Figure 10 and the reference numbers and operating conditions for this oxygen step are the same as those given for the oxygen step in Figure 10. Since the pulp should be washed in the oxygen treatment step, the oxygen step 430 after the third brown pulp scrubber is shown in Figure 11 to indicate its location after the batch digester, with no washing taking place in the digester. When using a bed cooker, there would be fewer brown pulp scrubbers and the oxygen phase could be earlier in the brown pulp system.

The following change is shown in bracket 431. This is a modification of the scrubber-oxygen system of Figure 11. There should be at least two washing steps after the oxygen white-35 summer step.

54 7 4 4 9 7 The two washing steps after the oxygen step at the corrugation 430 are scrubber 91 "'and the thickener 121', which has been converted to a scrubber. , then the oxygen system 431 could have been between the scrubber 91 "'and the storage tank 110", as shown in Figure 11.

In the system shown, thickener 121 'has been converted to a scrubber by adding spray heads 125, process water line 10 127 and a cleaning washer 124. The system has been further converted to an oxygen system by adding alkali line 425, steam mixer 426, steam line 427, oxygen mixer 429 and oxygen line 428. 'and the high pressure storage tank 140'. The operation is similar to that described in Figure 15.

The next change is in waveguide 432. This indicates, in dashed lines, the removal of chlorine and chlorine dioxide equipment. Chlorine dioxide mixer 144 ', chlorine dioxide tower 146', chlorine vacuum 153 ', chlorine mixer 155', chlorine tower 157 '20 and pump 159 have been removed. The piping and chemicals associated with this equipment have also been removed.

The next change is at corrugation 433. This corrugation indicates the removal of the extraction apparatus between scrubbers 161 'and 181' so that these scrubbers can be used as two washing steps after the oxygen phase at corrugation 431. This is also indicated by the parts shown in broken lines. The objects removed are the steam mixer 166 ', the extraction tower 173' and the pumps 170 ', 176', 278 'and 282'. Again, the piping and chemical additions required for the extraction step have also been removed. Pump 170 '30 may be maintained to transfer pulp 163' to scrubber 181 'if necessary.

The next two changes are shown in brackets 434 and 435. Bracket 434 indicates the removal of the chlorine dioxide step and the bracket 435 replaces it with a chlorine mixer. The removal of the chlorine dioxide stage results in the removal of the steam mixer 186 ', the chlorine dioxide mixer 191', the chlorine dioxide tower 193 'and the pumps 190', 196 ', 298 "and 302" and their associated piping and chemicals. These have been replaced by a small chlorine mixer 5a 438 and a chlorine supply line 151 '. A chlorine tower is not required. The pump 190 'is maintained if needed to transfer the pulp 183' to the mixer 430. The chlorine removal stream in line 294 "is kept separate from the oxygen removal stream.

The time in this mixer as well as the oxygen mixer-10 in sleep is less than 1 minute and normally it would be only a few seconds. A mass passing at a speed of 18.3 m / s would pass through a reactor 2, 4 or 3 m long in an unusually short time. Chlorine would be treated at a scrubber pulp temperature of 54-60 ° C rather than a colder chloro-15 scrubbing temperature.

The last change is shown in bracket 436. This is the addition of oxygen to the extraction step, as shown in Figure 9. The reference numerals and operating conditions are again the same as in Figure 9.

20 Each gas mixer should be under back pressure as described above.

Figure 13 shows another arrangement in which the bleaching series is OCODED. The changes between Figure 13 and Figure 1 are again shown in parentheses in Figure 13. The changes 431'-25 436 'are the same as the changes shown in Figure 12. In Figures 1, 12 and 13, the same reference numerals and operating conditions are used.

There is another change indicated by the bracket 437. This is the addition of E and D steps to the end-30 tree of the process. Again, the process conditions for this last extraction step are the same as for the other extraction steps and for this last chlorine dioxide step the same as for the other chlorine dioxide steps. It should also be understood that the only accessories required for these two steps are two additional washers. The extraction apparatus, 56 74497 omitted at 433 ', can be used in this extraction step and the chlorine dioxide apparatus removed at 434' can be used in this chlorine dioxide step. In the actual modification, this equipment could be left 5 in place and re-piped.

However, for purposes of this disclosure, reference numerals are used for these final steps.

In step E, the steam mixer is 446, the alkali line 447, the steam line 448, the sludge line 449, the pump 450, the extraction tower 453, the dilution zone 454, the line from the tower to the scrubber 455, and the pump 456.

In the extraction scrubber type 460, scrubber 461, drum 462, effluent 463, scrubber 464, incoming process water 490, spray heads 491, filtration line 492, shut-off tank 493, outlet flow line 494, dilution lines 495, 497 and 501 and their respective pumps 498 and 502, and a countercurrent wash water line 503 and its pump 504.

In the final chlorine dioxide stage, the steam mixer is 466, the alkali line 467, the steam line 468, the pulp slurry line 20,469, the pump 470, the chlorine dioxide mixer 471, the chlorine dioxide line 472, the chlorine dioxide tower 473, the dilution zone 476, and the line from the tower sulfur dioxide lines 477 and 478.

In the final scrubber, the type is 480, scrubber 481, 25 drum 482, effluent 483, scrubber 484, inlet process water 510, spray heads 511, filtration line 512, shut-off tank 513, drain line 514, dilution lines 515, 517 and 521 and their pumps 526, 51 and a countercurrent wash line 523 and its pump 524.

Again, each of the gas mixers should be back pressurized as described above.

The following two figures 14 and 15 illustrate the difference in equipment between a prior art bleaching plant with a DcEDED bleaching series and a plant using a system of the present invention with an OOCOD series. The Kum- 57 74497 pitch series starts with brown pulp washers and ends in the storage tank. The series shown in Figure 14 is the same as the DCEDED shown in Figure 1. The series in Figure 15 is the same as in Figure 12-00C0D. The reference numerals in Figs. 14 and 5 are the same as those used in Figs. 1 and 12 and refer to the same parts of the apparatus.

In Figure 14, the pulp 93 "" from the brown pulp scrubbers 28 "'is conveyed by a thick pulp pump 96" "to a high pressure storage tank 110" ". From the storage tank, the pulp slurry is transferred via line 111" "and pump 112" "to mixing tank 116 where it is mixed with water to reduce its consistency From the tank 116, the pump 117 conveys the pulp slurry via the line 118 to the sorters 113 "'. The pulp slurry 115 "'then enters the thickener 121"' where it is dewatered.

15 The filtrate passes through the filtration line 128 "to the" sealing tank 129 "", while the pulp 123 "'is transferred by a thick pulp pump 126" to the "high pressure storage tank 140"'.

The pulp from the high pressure storage tank 140 "'is transferred through line 141"' and pumps 142 "'and 156' and mixed with chlorine dioxide in tank 144" '. It then passes to the chlorine dioxide tower 146 "'and exits this tower via line 150 *. With the pulp in line 150', it mixes with the chlorine in mixer 155" 'and enters the chlorine tower 157 "'. The chlorinated material exits the chlorine tower 157" ' "'via line 158' and the foreign matter is washed out of it in scrubber 161" ". The filtrate passes through line 251" "to the sealing tank 253" '.

The pulp 163 "exits the scrubber, enters the steam mixer 166" and is mixed with sodium hydroxide and steam 30 and is passed through line 169 'by a thick pulp pump 170 "to the extraction tower 173". In this extraction step, as in the second, the alkali is added with a scrubber or steam mixer. The extracted pulp is transferred via line 175 'by pump 176 "' to scrubber 181" '. The filtrate from this washing step leaves via line 35 272 "' to sealing tank 273" '. The pulp 183 "' passes to a steam mixer 186" 'and is mixed again with steam and sodium hydroxide. It is then passed through line 189 'with a thick swab 190 "" to the chlorine dioxide mixer 191 "' and to the chlorine dioxide tower 193" '. The pulp slurry from the chlorine dioxide-5 di-tower is passed through line 195 "" by pump 196 "to scrubber 201" ". Again, filtrate from this scrubber is passed through line 292" "to seal tank 293" "while the exiting pulp 203" "passes to steam mixer 206" "for mixing with sodium hydroxide and steam and passed through line 209 "" with a thick pulp pump 210 "" to extraction tower 213 "".

From the tower, the slurry is passed through line 215 "" by pump 216 "" to scrubber 221 "" and washed. The filtrate exits the scrubber via line 312 "" to the shut-off tank 313 "" while mixing the pulp with steam and possibly sodium hydroxide in a steam mixer 226 "'. From the mixer, the pulp is passed via line 229" "to a thick gas pump 230"' chlorine dioxide mixer 23 "'and the chlorine dioxide tower 233"'. The pulp slurry is then passed through line 235 "" by pump 236 "'20 to scrubber 241"' where it is washed again. The filtrate passes through line 332 '"to the sealing tank 333"'. The pulp 243 "'is delivered by a thick pulp pump 450' via line 455 'to storage tank 527. From the storage tank, the material is conveyed by pump 528 via line 529 to some further processing.

25 This should be compared to the oxygen system shown in Figure 15. The eight storage tanks in the previous system will be converted to four storage tanks in this system. This figure could be reduced to three, as one chlorine dioxide tower in the system shown in Figure 15 can also be removed. Its purpose is to act as a storage tank within the system. It does not need to be used as a chlorine dioxide tower.

In both systems, the PBC of the material is the same at the beginning and also the same at the end. Thus, this result has been achieved with 35 major reductions in the cost of capital in this new system. At the same time, other savings are achieved.

59 74497

In the system shown in Figure 15, the pulp 93 "" "A from the brown pulp scrubbers 28" "is mixed with sodium hydroxide and steam in a steam mixer 106 'and passed through line 93" "" B by a thick pulp pump 96 ""' to oxygen-5 mixer 180 'and then line 93 "" "Via C to High Pressure Storage Tank 110" "'.

From this first oxygen stage, the pulp slurry is fed via line 111 "" 'by pump 112 ""' to tank 116 'and from there via line 118' by pump 117 'to sorters 113 "".

10 From the sorters, the mass 115 "" passes through the thickener 121 "". From the condenser, the filtrate is conveyed through line 128 "" to the shut-off tank 129 "", while pulp 123 "" A is introduced into steam mixer 426 ", mixed with sodium hydroxide and steam, and then passed through line 123" "B by a thick-mass pump 126 "" Oxygen Mixer 428 ". From the oxygen mixer, the material passes in line 123 "" C to the high pressure storage tank 140 "".

The pulp slurry from the high pressure storage tank is fed via line 141 "" by pump 142 "" to scrubbers 161 "" and 181 ". The filtrate from these two scrubbers passes through lines 252" "and 272" "20 to sealing tanks 253" "and 273" ", respectively. Pulp 183" " from scrubber 181 "" to pulp pump 190 "" to chlorine mixer 438 ". From the mixer, the slurry passes through line 195 "" to scrubber 201 "" '. From this scrubber, the filtrate passes through line 292 "" 'to the sealing tank 293 ""'. The pulp 203 "" 'is passed to a steam mixer 206 ""', mixed with sodium hydroxide and steam, and then conveyed in line 209 "" 'by a thick mass pump 210 ""' to an oxygen mixer 211 "'. From the oxygen mixer, the pulp passes through line 215" "' to scrubber 221" "'. The filtrate from this scrubber passes through line 312" "' 30 to the sealing tank 313" "'.

The pulp 223 "" 'from scrubber 221 ""' passes to a steam mixer 226 "", is mixed with sodium hydroxide and steam, and passed through line 229 "" through a thick pulp pump 230 "" through a thick pulp pump 230 "" to a chlorine dioxide mixer 351 "". From the mixer it passes to a 233 "" chlorine dioxide tower. This tower is optional.

60 74497

After the tower, the pulp slurry is fed through line 235 "" by pump 236 "" to scrubber 241 "". The filtrate from this scrubber passes through line 332 "" to the shut-off tank 333 "" and the pulp 243 "" is transferred by a thick pulp pump 450 "via line 5 455" to the storage tank 527 '. From this tank, it can be transferred by pump 528 'via line 529' to a subsequent operation.

In these figures, sodium hydroxide or other alkali can be added either with a scrubber or a steam mixer.

10 The scrubber after the mixer can be a diffuser.

Again, the mixer should have back pressure. This pressure is provided in the same manner as the pressure is applied to the mixer 211 by a vertical flow line, a pressure valve, or a combination thereof. The position of the valve and the maximum pressures are the same as for the mixer 211.

These illuminate the 0CO and OCO series and are examples of the O-O-X and O-X-O series in general. In either set, X may be chlorine, chlorine dioxide, a combination of chlorine or chlorine dioxide - CD, Dc, or a mixture of chlorine and chlorine dioxide, hypochlorites, peroxides, or ozone. The mixers described are used to mix these. The pulp can be treated with ozone by the treatment described in U.S. Patent Application No. 836,449, filed September 26, 1977, or U.S. Patent Application No. 2,491, dated January 11, 1979.

The amount of oxygen and chemicals used will, of course, depend on the K-number of the unbleached pulp, the desired brightness and the number of bleaching steps. As an example, in the OOCOD series, 14-20 kg of oxygen and 22-28 kg of sodium hydroxide-30 per ton of oven-dry pulp in the first stage would be used; 11-17 kg of oxygen and 17-22 kg of sodium hydroxide per tonne of kiln-dry pulp in the second stage, about 56 kg of chlorine per tonne of kiln-dry pulp in the third stage, 8-11 kg of oxygen per tonne of kiln-dry pulp in the fourth stage, and 14-16 kg of chlorine dioxide per tonne 61 74497 per oven dry mass in the last stage. The temperature of the pulp would not change from the temperature of the scrubber for chlorine treatment.

The other figures show several types of mixers that could be used in these systems. The exterior is similar in everyone; but the internal structure varies nonetheless.

In Figures 16-19, agitator 550 has a cylindrical body 551 and two end plates 552 and 553. Pulp slurry enters 10 through line 554, passes through agitator body, and exits line 555. Oxygen tubes 558 that supply oxygen to stators 530 inside the agitator are supplied by oxygen lines 559.

The shaft 560 runs in the longitudinal direction of the agitator and is supported on bearings 561 and 562 and is rotated by an actuator 563. The figure shows a chain drive but some other type of actuator can also be used.

The rotors 570 are mounted on a shaft 560. A typical rotor structure is shown in Figures 20-21. The rotor 2Q 570 has a shaft 571 which tapers outwards from the shaft and has an elliptical cross-section. The preferred cross section is an ellipse. The main axis of the rotor is aligned according to the direction of rotation of the rotor. Both of its advantages at the trailing edges 572 and 573 have a radius of curvature between 0.5-25 15 mm. The radii are usually the same, although they do not have to be. If they are different, the leading edge has a larger radius than the trailing edge.

One modification is shown in Figures 22-23. A groove 574 is formed in the rake edge 573 'of the rotor. The width of the groove is about 0.1 0.1 mm. The groove may be coated with a water-repellent material.

The number of rotors and the speed of the rotors depend on the amount of pulp passing through the mixer and the consistency of the pulp passing through the mixer. The area swept by the rotors should be in the range 10,000-1,000,000 m2 / t 2 35 oven dry pulp. The preferred range is 25,000-150,000 m / t kiln-62 74497 o dry pulp. The optimum is considered to be about 65,400 m / t of oven-dry pulp. This range is defined by the formula 1440 Ώ3 (r. 2-r „2) ^ R) W) A = _ 5 t where o A = sweep area / tonne, m / t = outer radius of the rotor, m r2 = inner radius of the rotor, m 10 R = rotor speed, r / min N = number of rotors t = tonnes (calculated as oven dry) of mass passing through the mixer per day.

There is a relationship between the length of the individual rotors and the number of rotors 15. The rotors are usually arranged in rings on the central shaft. The number of rotors in the ring depends on the circumference of the central shaft and the size of the rotor base. A larger number of rotors would require a longer and stiffer shaft. A smaller number of rotors 20 would require longer rotors. Thus, the space for the mixer would determine the actual rotor shape. Normally there are a total of 4-400 rotors and 2-20 rotors in the ring.

The rotors rotate perpendicular to the movement of the pulp through the mixer, forming a helical path 25 through the pulp. The rotational speed of the rotors would be determined by the motor and the gear ratio between the motor and the central shaft.

The diameter of the central shaft 560 is at least half the inner diameter of the mixer, forming a ring space 568 through which the slurry passes.

The enlarged shaft requires scraper bars 564 and 565 at the shaft ends 566 and 567. Normally there would be 4 bars at each end. The rods remove fibers that tend to accumulate between the shaft and the agitator end plate. This prevents the 35 shafts from getting stuck in the mixer.

63 7 4 4 9 7

The stators are shown in Figures 24-26. The stators add oxygen to the pulp in the mixing zone and also act as friction devices to reduce or prevent rotation of the pulp with the rotors so that there is a mutual rotational movement between the rotors and the pulp. Each stator 580 has a body 581, a center passage 582, and a base plate 583. The stators project into the body 551 through openings 556. There are two ways to attach stators. In Figure 24, the stator is attached to the body 551 by a friction attachment 10 using a Van Stone flange 584. This allows the stator to be rotated if the oxygen placement is to be changed. In Figure 25, the base plate 583 'is attached directly to the body 551 with either bolts or stud screws. Oxygen enters the mixer through the shut-off valves 590. The stato-15s are round and tapered and the surface on which the shut-off valves are flattened. The shut-off valves open across the transverse plane of the mixer and in the direction of rotation of the rotors.

The purpose of the shut-off valve 590 is to prevent pulp-20 fibers from entering the passageway 582. A typical shut-off valve is shown in Figure 27. The valve 590 comprises a valve body 591 threaded to the stator body 581. The valve body has a valve seat 592. The valve itself comprises a bolt 594 and nut , which spring 595 pushes 25 to the closed position.

The number of shut-off valves in the stator varies from 0 to 4. In some mixers, most of the gas is added at the mixer inlet, requiring shut-off valves up to four, and little or no gas would be added near the mixer outlet, requiring one shut-off valve or no valve, and the stators would then act only as a frictional brake against mass rotation. For example, 60-70% oxygen could be added in the first half of the mixer. The first third of Staat-35 markets could have three or four shut-off valves, the next third could have 74497 64 2 shut-off valves, and the last third could have one or no valves.

The stators are also arranged in rings. For each one or two rings of rotors there is one ring with 5 stators. The number of stators in the ring depends on the size of the mixer. There are usually four stators in a ring, but this can normally range from 2 to 8.

Both rotors and stators should extend across the ring space. The normal clearance between the rotor and the inner wall of the agitator or the outer wall of the stator and the central shaft is about 13 mm. This ensures that all the pulp comes into contact with oxygen and that no short bypass can be created for the pulp through the mixer without contact with oxygen. The rotors and stators should be between the si-15 inlet and outlet to ensure that all mass passes through the swept area and comes into contact with oxygen.

Figures 28-33 show a modification of the basic mixer. Oxygen is introduced into the rotors via line 600 and passageway 601 running through the center of shaft 560 '. The radial passages 602 carry oxygen to the outer annular manifold 603. Oxygen passes from the manifold to the pulp through the center passage 604 of the rotor arm 605 and through the shut-off valve 590 ". These valves are similar to the valve 590.

25 The rotor is shown as round and tapered, but may have a different shape. The rotor can be round or rectangular and not tapered, like the rotors usually found in steam mixers. The radii of curvature of round rotors would be more than 30 mm. It is also possible to use tapered rotors 606 with a rectangular cross section.

Fig. 34 compares the operation of a modified mixer similar to that shown in Figs. 28-33 to the operation of the mixer of Figs. 16-27 and shows the increased power of the mixer as the sweep range increases and the shaft through-35 dimension is increased. The jacket of both mixers was 65 65 4 4 9 7. Its internal pressure was 0.914 m. The entrance and exit were similar. The external radius of each rotor was the same, 0.444 m. Each handled the same amount of pulp, 810 tons of oven-dried pulp per day.

5 The speed of the converted mixer was 435 rpm.

There were 32 stators in 8 rings and 36 rotors in 9 rings. Each rotor ring had 2 pins and 2 blades. The blades were rectangular in cross section.

The stators and rotor rods were round, tapering outwards and 0.254 m long. Oxygen was only passed through the stators. The shaft diameter was 0.38 m and the swept 2 area was 14,100 m / t of oven-dry pulp.

The agitator of Figures 16-27 had the same inside diameter, but had a central shaft diameter of 0.508 m. There were 224 rotors. The rotors were elliptical and linearly tapered. The main axis of the rotor ran in the direction of rotation of the rotor. The radii of curvature of the front and rear edges of the rotor were 3.8 mm. The rotors were 19 cm long and extended about 13 mm from the reactor wall and the stators extended about 2 mm from the central axis. The rotation speed of the rotors was 435 rpm. The swept area of the reactor was 72,200 m / t of oven-dried pulp. Oxygen was passed through the stators.

Figure 34 compares the K-number of the extracted pulp with the additional drop of K-number 25 after the pulp has passed through the mixer, and this indicates that the mixer caused a greater decrease in K-number than the modified mixer. It was also found that the mixer required only half the amount of oxygen compared to the modified mixer to reach the same amount of lignin removal; i.e., while other operating conditions remained the same, 11 kg of oxygen / t of oven-dried pulp was required in the modified mixer to achieve the same reduction in K-number, but only 5 kg of oxygen / t of oven-dried pulp was needed in the mixer. It was also found that the mixer was able to mix larger amounts of oxygen with the pulp than the modified 66 744 9 7 mixer. About 1.5-2 times as much oxygen could be mixed with the pulp with a mixer as with a modified mixer. For example, a modified mixer was able to mix up to 15.1-20.2 kg of oxygen per ton with 5 oven-dry pulp. The mixer was able to mix 30.2-35.3 kg of oxygen with a ton of oven-dry pulp.

The optimum sweep area is achieved by reducing the number of rotors in the mixer from 224 to 203 re.

Figures 35-37 illustrate different types of rotor and 10 stator arrangements and different ways of conducting oxygen.

In this variation, the oxygen supply line 610 surrounds the outer body 551 of the mixer and the gas enters the mixer through holes 611 in the body 551 ". An annular barrier wall 612 interposed between each ring of holes 611 is attached to the inner wall of the body 551". The barrier walls 612 form a gas collection near the agitator wall. The stators 585 are attached to the barrier walls 612. The rotors 575 are arranged in rows parallel to the spaces between the barrier walls 612. The outer radius of the rotors 575 is greater than the inner radius of the barrier walls 612, so that the rotors extend behind the barrier wall 608 into the trapped gas between the locks. The design allows the rotor to extend into the gas pocket and the gas to flow along the rear edge of the rotor as it passes through the pulp slurry.

25 Rotors and stators can be flat, front and rear edges rounded. Again, the radius of curvature of the leading and trailing edges would be between 0.5 and 15 mm and these radii need not be the same. The rotors and stators can be as narrow as 6.35 miti wide.

30 This structure could also include a groove in the rotor of the rotor, which may be covered with a water-repellent coating.

Claims (18)

67 74497 A method for mixing a chemical with a wood pulp having a consistency of 7-15%, wherein the chemical is an uncondensed gas, an unsaturated gas or a highly superheated steam, and wherein the chemical is introduced into a pulp in a mixing zone, characterized in that the mixing zone has a series of pulp rotating members having a main axis 10 extending in the direction of rotational movement and having front and rear edges, the rotating members passing through the mass transverse to the direction of travel of the mass and having a sweep area through the mass 2 of 10,000 to 1,000,000 m / t oven-dry mass, and 15 wherein the radius of curvature of the leading edge is 0.5 to 15 mm. Method according to Claim 1, characterized in that the sweeping area is 14,000 to 1,000,000 m 2 / t of oven-dry pulp. Method according to Claim 1, characterized in that the sweeping area is from 25,000 to 150,000 m 2 / t of oven-dry pulp. A method according to claim 1, characterized in that the sweeping area is about 2,645,400 m / t of oven-dry pulp. Method according to one of the preceding claims, characterized in that the radius of curvature of the trailing edge is 0.5 to 15 mm. Process according to one of the preceding claims, characterized in that the chemical is increasingly added to the pulp. Method according to one of Claims 1 to 5, characterized in that the mixing takes place at a pressure of at most 830 kPa. Process according to one of the preceding claims 35, characterized in that the cabbage is oxygen, ozone, air, chlorine, chlorine dioxide, sulfur dioxide, ammonia, nitrogen, carbon dioxide, hydrogen chloride, nitrogen oxide or nitrogen peroxide. Mixer for use in a method according to any one of the preceding claims 5, comprising a housing with inlet and outlet, shaft and mixing zone, characterized in that the shaft (560) has a plurality of rotors (570) in the mixing zone with front and rear edges (572). , 573), wherein the radius of curvature of the leading edge (572) is 0.5 to 15 mm, and wherein the rotors (570) are rotatable through the slurry transversely to the direction of travel of the slurry and have a sweep area of 10,000 to 1,000,000. m / t of oven-dry solid in the slurry. Agitator according to Claim 9, characterized in that the sweeping surface area of the rotors (580) is 14,100 to 1,000,000 m / t of oven-dry solids in the slurry. Agitator according to Claim 9, characterized in that the sweeping area of the rotors (570) is 25,000 to 150,000 m 2 / t of oven-dry solids in the slurry. Agitator according to claim 9, characterized in that the sweeping area of the rotors (570) is about 65,400 m / t of oven-dry solids in the slurry. Agitator according to one of Claims 9 to 12, characterized in that the rotors (570) have elliptical cross-sections and a main axis extending in the direction of rotation. Agitator according to one of Claims 9 to 12, characterized in that the mixing zone is an annular space (568), the radius of the inner surface of the space (568) being at least half the radius of the outer surface 35 of the space (568). Agitator according to one of Claims 9 to 12, characterized in that the radius of curvature of the rear edge (573) is 0.5 to 15 mm. 69 7 4 4 9 7 Agitator according to Claims 9 to 12, characterized in that the rear edge (573 ') has a groove (574) which runs in the longitudinal direction of the rear edge (573'). Agitator according to Claims 9 to 12, characterized in that the rotors (570) taper outwards. Agitator according to claim 9 or 12, characterized in that it comprises a plurality of stators (580) extending from the housing (551) to the agitation zone, at least some of the stators (580) having a first passageway (582) extending longitudinally from outside the agitation zone. (580), and a second passageway 15 communicating with the first passageway (582) and the mixing zone, and a shutoff valve (590) in the second passageway. 70 7 4 4 9 7