Abstract: A system and method for improved filtrate addition in a continuous digester is disclosed. The system comprises a blow dilution header/nozzle assembly located in the blow dilution zone of the digester. The header/nozzle assembly comprises (i) a plurality of nozzles for introducing and distributing filtrate into the blow dilution zone, and (ii) a plurality of measurement and control devices for monitoring and controlling filtrate flow through the plurality of nozzles. The method comprises (a) introducing and distributing filtrate through a plurality of nozzles of a blow dilution header/nozzle assembly in the blow dilution zone of the continuous digester; and (b) measuring and controlling the filtrate flow through each nozzle of the plurality of nozzles.

Abstract: Systems, methods, and vessels for reducing the stagnation and non-uniform flow or treatment of solid materials and slurries in vessels. The non-uniform flow or treatment that may characterize the storage or treatment of solid materials in process industries is minimized or eliminated by the introduction of liquid to the bottom heads of the vessels, in particular, the introduction of liquids in regions in the bottom heads where friction and compression cause stagnation in the flow of material. The liquid may be introduced by means of one or more nozzles, for example, one or more evenly-spaced nozzles, and the flow of liquid to each nozzle may be individually controlled. Though the systems, methods, and vessels disclosed may be used in the processing of cellulose materials, aspects of the present invention may be used in any process or materials handling industry application where solid materials or slurries are handled in vessels.

Abstract: A continuous digester configuration and process for continuously cooking and digesting cellulosic material and producing cellulosic pulp is disclosed. The digester configuration comprises a plurality of jump-stage recirculations located along the length of a continuous digester vessel, wherein each of the jump-stage recirculations moves extracted liquor from one elevation of the digester vessel and re-introduces the liquor at a higher elevation in the vessel to maintain an internal liquor downflow substantially throughout the entire digester vessel. The process for continuously cooking and digesting cellulosic material comprises maintaining an internal concurrent liquor downflow substantially throughout the continuous digester vessel, wherein the internal liquor downflow does not exceed 400 gallons per ton of b.d. wood feed.

Abstract: A system and method for improved filtrate addition in a continuous digester is disclosed. The system comprises a blow dilution header/nozzle assembly located in the blow dilution zone of the digester. The header/nozzle assembly comprises (i) a plurality of nozzles for introducing and distributing filtrate into the blow dilution zone, and (ii) a plurality of measurement and control devices for monitoring and controlling filtrate flow through the plurality of nozzles. The method comprises (a) introducing and distributing filtrate through a plurality of nozzles of a blow dilution header/nozzle assembly in the blow dilution zone of the continuous digester; and (b) measuring and controlling the filtrate flow through each nozzle of the plurality of nozzles.

Abstract: Kraft pulp of increased strength and bleachability may be produced with decreased consumption of effective alkali, and at a lower H factor, by keeping the dissolved organic material (DOM) concentration low substantially through the entire kraft cook, including by extracting high DOM liquid from at least one part of a continuous digester and replacing it with much lower level DOM liquid. Existing pulp mills having two-vessel hydraulic, one-vessel hydraulic, or other systems may be retrofit to provide for extractions and additions of low DOM dilution liquor (including substantially DOM-free white liquor). Also, commercial size batch digesters (8 tons per day of pulp or more) can be operated with low DOM liquor to produce increased strength pulp. Using dilution with low DOM liquor also results in reduced H factor and effective alkali consumption, and increased bleachability.

Abstract: In the production of chemical pulp, such as kraft pulp, it is possible to reduce the amount of ancillary equipment, and/or the size of the continuous digester vessel, while achieving enhanced uniformity of treatment by avoiding “hang ups”. Instead of providing vertical counter-current flow of liquid and comminuted cellulosic fibrous material being treated in the lower half of the digester, the counter-current flow may be a cross flow, that is substantially horizontal (e.g. radial) while the flow of the chip column is vertical. Regardless of the configuration of the digester vessel, a single pump may be utilized for all of the recirculations, or only a few pumps for all of the recirculations.

Abstract: Kraft pulp of increased strength and bleachability may be produced with decreased consumption of effective alkali, and at a lower H factor, by keeping the dissolved organic material (DOM) concentration low substantially through the entire kraft cook, including by extracting high DOM liquid from at least one part of a continuous digester and replacing it with much lower level DOM liquid. Existing pulp mills having two-vessel hydraulic, one-vessel hydraulic, or other systems may be retrofit to provide for extractions and additions of low DOM dilution liquor (including substantially DOM-free white liquor). Also, commercial size batch digesters (8 tons per day of pulp or more) can be operated with low DOM liquor to produce increased strength pulp. Using dilution with low DOM liquor also results in reduced H factor and effective alkali consumption, and increased bleachability.

Abstract: In the production of chemical pulp, such as kraft pulp, it is possible to reduce the amount of ancillary equipment, and/or the size of the continuous digester vessel, while achieving enhanced uniformity of treatment by avoiding “hang ups”. Instead of providing vertical counter-current flow of liquid and comminuted cellulosic fibrous material being treated in the lower half of the digester, the counter-current flow may be a cross flow, that is substantially horizontal (e.g. radial) while the flow of the chip column is vertical. Regardless of the configuration of the digester vessel, a single pump may be utilized for all of the recirculations, or only a few pumps for all of the recirculations.

Abstract: Chemical cellulose pulp (e.g. kraft pulp) is produced with enhanced strength and/or yield using a strength or yield enhancing additive such as polysulfide or anthraquinone or its equivalents or derivatives, and in a manner that allows effective recovery/reuse of the additive so as to make the process more economical. In a continuous digester a low temperature and relatively low alkalinity protecting zone is provided at the top of the digester terminating with a first screen, and a second screen is provided below the first screen. Between the first and second screens, prior to bulk delignification, a first counter-current zone is provided, and additive-containing liquid from the first screen is recirculated to the slurry at or near the digester inlet to enhance yield or strength.

Abstract: Kraft pulp of increased strength and bleachability may be produced with decreased consumption of effective alkali, and at a lower H factor, by keeping the dissolved organic material (DOM) concentration low substantially through the entire kraft cook, including by extracting high DOM liquid from at least one part of a continuous digester and replacing it with much lower level DOM liquid. Existing pulp mills having two-vessel hydraulic, one-vessel hydraulic, or other systems may be retrofit to provide for extractions and additions of low DOM dilution liquor (including substantially DOM-free white liquor). Also, commercial size batch digesters (8 tons per day of pulp or more) can be operated with low DOM liquor to produce increased strength pulp. Using dilution with low DOM liquor also results in reduced H factor and effective alkali consumption, and increased bleachability.

Abstract: Kraft pulp of increased strength and bleachability may be produced with decreased consumption of effective alkali, and at a lower H factor, by keeping the dissolved organic material (DOM) concentration low substantially through the entire kraft cook, including by extracting high DOM liquid from at least one part of a continuous digester and replacing it wit much lower level DOM liquid. Existing pulp mills having two-vessel hydraulic, one-vessel hydraulic, or other systems may be retrofit to provide for extractions and additions of low DOM dilution liquor (including substantially DOM-free white liquor). Also, commercial size batch digesters (8 tons per day of pulp or more) can be operated with low DOM liquor to produce increased strength pulp. Using dilution with low DOM liquor also results in reduced H factor and effective alkali consumption, and increased bleachability.

Abstract: A method of controlling the pressure of a vertical continuous comminuted cellulosic fibrous material (wood chip) digester is provided using a pressure-control extraction in a zone relatively insensitive to changes in the flow rate of liquid introduction or removal. The method comprises controlling the pressure in the digester primarily (or substantially exclusively) by varying the flow rate of liquor extracted from the pressure-control extraction to maintain the pressure in the digester at a desired superatmospheric level while avoiding non-uniform, unstable material movement in the counter-current washing zone; and introducing dilution liquid into the digester at the at least one recirculation-dilution loop. The pressure-control extraction is preferably substantially the upper extraction in the digester. Substantially except during excessive over pressure and under pressure conditions the extraction flow from the main extraction is maintained substantially constant.

Abstract: A system and method for feeding comminuted cellulosic fibrous material such as wood chips to the top of a treatment vessel such as a continuous digester provide enhanced simplicity, operability, and maintainability by eliminating the high pressure transfer device conventionally used in the prior art. Instead of a high pressure transfer device the steamed and slurried chips are pressurized using one or more slurry pumps located at least thirty feet below the top of the treatment vessel and for pressurizing the slurry to a pressure of at least about 10 bar gauge. A return line from the top of the digester may, but need not necessarily, be operatively connected to the one or more pumps and if connected to the pumps the pressure in the return line may be reduced utilizing a pressure reduction valve and/or a flash tank.

Abstract: Kraft pulp of increased strength and bleachability may be produced with decreased consumption of effective alkali, and at a lower H factor, by keeping the dissolved organic material (DOM) concentration low substantially through the entire kraft cook, including by extracting high DOM liquid from at least one part of a continuous digester and replacing it with much lower level DOM liquid. Existing pulp mills having two-vessel hydraulic, one-vessel hydraulic, or other systems may be retrofit to provide for extractions and additions of low DOM dilution liquor (including substantially DOM-free white liquor). Also, commercial size batch digesters (8 tons per day of pulp or more) can be operated with low DOM liquor to produce increased strength pulp. Using dilution with low DOM liquor also results in reduced H factor and effective alkali consumption, and increased bleachability.

Abstract: In a vertical digester for producing chemical pulp, or other vessel for treating a slurry of comminuted fibrous cellulosic material, the cost of manufacturing the shell is significantly reduced by eliminating the external step increases in the digester shell. The digester shell has a substantially constant internal diameter from just below the inlet to just above the outlet, screen assemblies being provided by an internal transition (e.g. conical) having an angle of convergence of less than 40.degree. (e.g. about 10-25.degree.) above each screen assembly so that the slurry flows through the transition without bridging or hang-up, and a step increase, or other increase, in diameter back to the first diameter after the screen assembly.

Abstract: A method of treating wood chips allows chemical pulp (e. g. kraft pulp) to be produced having enhanced fiber strength properties. In a first zone or stage the chips are cool impregnated (e. g. a temperature of about 60-120.degree. C.) with a first alkali-containing liquid (25-35 g/l expressed as NaOH). In the top of a continuous digester in a second zone or stage the chips are then treated with a second alkali-containing liquid having an alkali concentration at least 5 g/l less than the first liquid (e. g. 10-20 g/l) and a temperature of between about 120-160.degree. C. (e. g. 130-150.degree. C.). An extraction typically takes place to effect the change in treatment zones. After the second zone the chips are cooked at about 140-180.degree. C. (e. g. 150-170.degree. C.), and higher than in the second zone.

Abstract: Kraft pulp of increased strength and bleachability may be produced with decreased consumption of effective alkali, and at a lower H factor, by keeping the dissolved organic material (DOM) concentration low substantially through the entire kraft cook, including by extracting high DOM liquid from at least one part of a continuous digester and replacing it with much lower level DOM liquid. Existing pulp mills having two-vessel hydraulic, one-vessel hydraulic, or other systems may be retrofit to provide for extractions and additions of low DOM dilution liquor (including substantially DOM-free white liquor). Also, commercial size batch digesters (8 tons per day of pulp or more) can be operated with low DOM liquor to produce increased strength pulp. Using dilution with low DOM liquor also results in reduced H factor and effective alkali consumption, and increased bleachability.

Abstract: Digester systems for producing paper pulp from comminuted cellulosic fibrous material take into account the level of dissolved organic materials (DOM), such as lignin, hemi-cellulose, and cellulose, maintaining the DOM level at about 100 g/l throughout the cook (particularly kraft cook). In order to make sure there is sufficient liquid to slurry the material in the feed system of a two vessel system, some liquid is withdrawn from the circulation conduits between the digester and impregnation vessel, cooled, and fed to the feed system. In a vapor phase digester, the level of liquid at the top of the digester is more precisely controlled by circulating some of the withdrawn liquid from a circulatory loop of the digester to the level tank associated with the feed system. An in-line drainer may be provided in the feed system between a make-up liquor pump and a liquid inlet conduit leading to the top of an impregnation vessel.

Abstract: The sulfide ion concentration and sulfidity of kraft cooking liquor during kraft cooking of cellulose pulp is selectively increased. After treatment in a first treatment zone in which impregnation or kraft cooking takes place using a kraft cooking liquor having a first sulfide ion concentration and sulfidity, black liquor is extracted from the material, liquid is withdrawn from the material and dilution liquid is added to the withdrawn liquid and the withdrawn liquid with dilution liquid is reintroduced. In a second treatment zone after the first zone a second kraft cooking liquor is introduced having a second sulfide ion concentration and sulfidity greater than the first sulfide ion concentration and sulfidity (typically by about 20-50%), including by manipulating controlling the flow rate of extraction and the flow rates of withdrawal of liquid and addition of dilution liquid.

Abstract: A number of distinct parallel digesters are fed with chips from a common steaming vessel. After steaming the chips are slurried and pressurized, and substantially simultaneously the steamed, slurried, and pressurized chips are transferred to at least some of (and typically each of) the distinct parallel digesters. A material stream is split into a number of individually controllable material streams (one for each of the digesters) either at the discharge from the steaming vessel, after slurrying (or at the discharge from a slurrying vessel), or after pressurizing (e.g. in a high pressure transfer device). For example a multi-branch conduit may be connected to the slurry outlet from the high pressure transfer device, the conduit having a branch directly connected to each of the digesters. A distinct return conduit may also be provided from each of the digesters to the high pressure transfer device, each return conduit preferably has a distinct flow control device and/or pump which are individually controlled.