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  System and method for oxygen delignification of pulp made for lignocellulosic materialUSPTO Application #: 20060169429Title: System and method for oxygen delignification of pulp made for lignocellulosic material Abstract: The system is for the oxygen delignification, in at least two reaction stages, of pulp that consists of lignocellulose-containing material having a mean concentration of 8-18% pulp consistency. The system has a first pump followed by a first oxygen mixer that is followed by a first delignification zone. The first delignification zone is followed by a second steam mixer that is followed by a second pump that is followed by a third oxygen mixer and a second delignification zone. (end of abstract)
Agent: Fasth Law Offices (rolf Fasth) - Southern Pines, NC, US Inventors: Hakan Dahloff, Martin Ragnar USPTO Applicaton #: 20060169429 - Class: 162065000 (USPTO) Related Patent Categories: Paper Making And Fiber Liberation, Processes Of Chemical Liberation, Recovery Or Purification Of Natural Cellulose Or Fibrous Material, Gas, Vapor Or Mist Contact, Oxygen, Ozone Or Air The Patent Description & Claims data below is from USPTO Patent Application 20060169429. Brief Patent Description - Full Patent Description - Patent Application Claims
PRIOR APPLICATIONS [0001] This application is a U.S. national phase application based upon International Application No. PCT/SE00/01435, filed 5 Jul. 2000; which claims priority from Swedish Application No. 9902586-8, filed 6 Jul. 1999. TECHNICAL FIELD [0002] The present invention relates to a system and a process for oxygen delignification. BACKGROUND AND SUMMARY OF THE INVENTION [0003] A number of different processes for oxygen delignification are known. For example, U.S. Pat. No. 4,259,150 presents a system with multistage oxygen bleaching in which, in each stage, the pulp is first mixed to a lower consistency with O.sub.2, water and NaOH, followed by a thickening back to the consistency level which the pulp had prior to the stage in question. The aim is to obtain an economic, chlorine-free bleaching with high yield. At the same time, the kappa number can be lowered, by means of repeated stages, from 70 down to 15 or even less than 15. [0004] Swedish Patent C,467.582 presents an improved system for the oxygen bleaching of pulp of medium consistency. By means of controlling the temperature in an optimized manner, an oxygen bleaching takes place in a first delignification zone at a low temperature, with this being followed by a second delignification zone at a temperature which is 20-40 degrees higher. The aim is to obtain an improved yield and an improved viscosity, while retaining the dwell time, in association with industrial use. [0005] Other variants of oxygen delignification in two stages have also been patented in addition to Swedish Patent No. C,467.582. Swedish Patent No. C,505.147 presents a process in which the pulp should have a high pulp concentration in the range of 25-40% in the first stage and a concentration of 8-16% in the second stage, at the same time as the temperature in the second stage should be higher than, or equal to, the temperature in the first stage, in line with the temperature difference which is recommended in Swedish Patent No. C,467.582. The advantages of the solution in accordance with Swedish Patent No. C,505.147 are stated to be the possibilities of admixing more oxygen in the first high-consistency stage without there being any risk of channel formation but where, at the same time, unused quantities of oxygen can be bled off after the first stage in order subsequently to be admixed in a second mixer prior to the second stage. [0006] Swedish Patent No. C,505.141 presents a further process which is an attempt to circumvent Swedish Patent No. C,467.582, since that which it is sought to patent is stated to be that a temperature difference between the stages does not exceed 20 degrees, i.e., the lower suitable temperature difference patented in SE,C,467.582, but that a temperature difference should nevertheless be present. In addition to that, it is stated that a) the pressure should be higher in the first stage and b) that the dwell time is short in the first stage, i.e., in the order of magnitude of 10-30 minutes, and also c) the dwell time in the second stage is longer, i.e., in the order of magnitude of 45-180 minutes. [0007] A lecture entitled "Two stage MC-oxygen delignification process and operating experience" which was given by Shinichiro Kondo from the Technical Div. Technical Dept. OJI PAPER CO. Ltd. At the 1992 Pan-Pacific Pulp & Paper Technology Conference, 99 PAN-PAC PPTC, Sep. 8-10, Sheraton Grande Tokyo Bay Hotel & Towers, presents a successful installation which was constructed with two-stage oxygen delignification in 1986 in a plant in Tomakomai. [0008] In this OJI PAPER plant in Tomakomai, the pulp was fed, with a pressure of 10 bar, to a first oxygen mixer (+team) followed by an after-treatment in a pre-retention tube (pre-reactor), with a 10 minute dwell time in which the pulp pressure is reduced to a level of about 8-6 bar due to pipe losses, etc. After that, the pulp was fed to a second oxygen mixture followed by an after-treatment in a reactor at a pressure of 5-2 bar and with a dwell time of 60 minutes. It was stated at this point that preference would have been given to having a pre-retention tube which would have given a dwell time of 20 minutes but that it was not possible to construct this due to lack of space. The OJI PAPER stated that, by using this installation, they had succeeded in obtaining an increase in kappa reduction at a lower cost in chemicals and with the pulp viscosity being improved. [0009] Most of the prior art has consequently been directed towards a higher pressure in the first reactor at a level of about 6(8)-10 bar. A pressure in the first reactor of up to 20 bar has even been discussed in certain extreme applications. This results in it being necessary to manufacture the reactor spaces which are required for the first delignification zone such that they can cope with these high pressure levels, with a consequent requirement for substantial material thickness and/or good material qualities, which in turn result in an expensive installation. [0010] In pulp suspensions in industrial production processes, there are large quantities of readily oxidizable constituents/structures which already react under modest process conditions. It is therefore advantageous, in a first stage, to add oxygen in quantities which are such that this part of the pulp which is relatively easily oxidized is allowed to oxidize/react first of all. Severe problems arise if an attempt is made to compensate for this by over-adding oxygen since there is the immediate danger of canalization problems, as mentioned in Swedish Patent No. C,505.147. [0011] One object of the present invention is to avoid the disadvantages of the prior art and to obtain an oxygen delignification which gives increased selectivity. The present invention permits an optical practical application of the theories regarding a first rapid phase and a second slower phase during the oxygen delignification process, with the optimal reaction conditions being different between the phases. [0012] At the high hydroxide ion concentrations and high oxygen partial pressures which are conventionally employed in the first stage, the carbohydrates are attacked more than is necessary, thereby impairing the quality of the pulp. A lower oxygen partial pressure, and preferably a lower temperature as well, in the first stage as compared with the second stage decreases the rate of reaction for the breakdown of carbohydrates more than it decreases the rate of reaction for the delignification, leading in turn to an increase in the total selectivity on the pulp after the two stages. [0013] Another object of the present invention is to allow a simpler and cheaper process installation in which at least one pressure vessel, in a first delignification zone, can be manufactured using thinner material and/or using a lower material quality which is suitable for a lower pressure class. [0014] Yet another object is also to make it possible to use steam at moderate pressure especially when there is a need to increase the temperature substantially between the first and second stage and when the pressure in the second stage is considerably higher than that in the first stage. In most cases, the supply of medium-pressure steam and low-pressure steam is very good in a pulp mill whereas high-pressure steam is in short supply due to the large number of processes which require high-pressure steam. This also makes it possible to convert existing single-vessel delignification systems where, with the previously the prior art for converting to a two-stage design, a restriction has been imposed by the fact that the prevailing pressure in the plant's steam grid has not enabled a sufficiently large quantity of steam to be admixed with the pulp in order to achieve the desired temperature in the second delignification stage. [0015] Yet another object is to optimize the mixing process in each position such that only that quantity of chemicals/oxygen is added which is consumed in the subsequent delignification zone and where the admixture of chemicals/oxygen does not need to compete with the simultaneous admixture of steam for the purpose of increasing the temperature to the desired level. In this way, it is possible to dispense with bleeding systems for overshooting quantities of oxygen at the same time as it is possible to reduce the total consumption of oxygen, which in turn reduces the operating costs for the operator of the fibre line and thus shortens the pay-off time. At the same time, it is possible to select a smaller size of dynamic mixer for admixing chemicals, which mixer is dimensioned solely for the volumes of chemicals which are actually being admixed. [0016] Yet another object is to increase, in an oxygen delignification system having a certain total volume of the first and second stages, a so-called H factor by operating the first stage for a short time at low temperature and operating the second stage for a longer time at a higher temperature. Thus, in connection, for example, with conversions of existing single-vessel oxygen delignification stages, a simple conversion, including a small pre-reactor and a modest increase in the reaction temperature in the existing reactor, can increase the H factor and at the same time improve the selectivity over the oxygen stages. BRIEF DESCRIPTION OF THE DRAWINGS [0017] FIG. 1 shows a system for oxygen delignification in two stages in accordance with the invention; and [0018] FIG. 2 diagrammatically shows the kinetics of the oxygen delignification and the advantages which are gained relative to the prior art with regard to reduction in kappa number and an increased H factor. DETAILED DESCRIPTION [0019] FIG. 1 shows an installation, according to the present invention, of a system in an existing plant in which the oxygen delignification process needed upgrading. Continue reading... Full patent description for System and method for oxygen delignification of pulp made for lignocellulosic material Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this System and method for oxygen delignification of pulp made for lignocellulosic material patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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