Abstract: A method for conditioning an ozone gas recycle stream in an ozone pulp bleaching process. The method includes the steps of providing an oxygen containing feed gas to an ozone generator; generating ozone from said feed gas to produce an ozone rich oxygen gas; bleaching pulp with said ozone rich gas, thereby producing an exhaust gas containing contaminants including carbon dioxide and entrained pulp fibers; removing at least some of said contaminants by at least removing entrained pulp fibers from the exhaust gas to produce a recycle gas; directing said recycle gas into the ozone generator to provide at least a portion of said oxygen containing feed gas; and removing carbon dioxide during said contaminant removal step in an amount sufficient to a level of about 6 wt. wt. % to thus allow operation of the ozone generator at or approaching full capacity.

Abstract: A process for conditioning an ozone gas recycle stream in an ozone pulp bleaching process, wherein the level of carbon dioxide in the recycle stream is controlled to allow full capacity operation of the ozone generator. Carbon dioxide concentration is identified over the relevant operational ranges and maximum concentration is identified for full capacity/optimum efficiency operation. Specific methods are described for controlling carbon dioxide concentration including purging a portion of the recycle stream, counter-current scrubbing of the recycle stream with an alkaline solution and passing the recycle stream through an adsorbent material. Contaminants entering the system also may be reduced by directing the purged recycle stream, which is relatively oxygen rich, into the dewatering press where pulp consistency is increased. In this manner nitrogen surrounding the pulp is displaced by oxygen and thus, does not enter the bleaching/ozone system with the pulp.

Abstract: A two stage ozone-pulp bleaching method and apparatus are disclosed. In the first stage, high consistency pulp particles are turbulently mixed and contacted with a gaseous mixture containing ozone to mix and contact substantially all of the pulp particles with ozone to react at least a portion of the pulp particles with the ozone. Pulp particles and gaseous bleaching mixture are then directed to a second stage including a quiescent pulp bed. Pulp particles may complete their reaction in the bed, which also serves to strip ozone which was not contacted with pulp particles in the first stage from the gaseous bleaching mixture.

Abstract: An apparatus for delignifying and bleaching a lignocellulosic pulp without the use of elemental chlorine. The bleaching reactor is a horizontal vessel having a central rotatable shaft which preferably contains paddles, cut and folded screw flights or a ribbon flight, to disperse and advance the pulp particles in a plug flow manner while contacting and mixing the pulp particles with a gaseous bleaching agent such as ozone for substantially uniform bleaching thereof.

Abstract: An improvement is disclosed for a boiler leak system that (a) measures fluid input into the recovery boiler system, (b) measures fluid output from the recovery boiler system, and (c) calculates fluid leakage loss based on an average difference between the measured fluid input and output values. The improvement increases the accuracy and responsiveness of calculating and interpreting the difference between the input and output fluid flow of the boiler. One aspect of the invention is an improved method which includes (1) compensating for the effects of boiler drum swelling and shrinking; (2) using multiple time frames to calculate the average differences between input and output such that a balance is struck between a highly responsive leak indication (short time frame) and a highly accurate leak indication (longer time frame); and/or (3) indicating a leak only after a predetermined certain sequence of significant differences between input and output is reached.

Abstract: A process control method for adjusting chemical application in response to the pulp brightness and/or lignin content is realized by utilizing a coupled control feedforward, feedback or combination feedforward/feedback control system, wherein brightness measurements are made between successive lignin content measurements and adjustments made to the chemical application in response to a comparison value.

Abstract: The use of hot water extraction (pH 7-8, 165.degree. F.) in place of an alkaline extraction in pulp bleaching sequences between an ozone delignification stage alkaline wash and a brightening stage allows higher strength pulp to be achieved at essentially the same brightness levels using reduced overall amounts of bleaching chemicals. In addition, effluents from pulp washing stages following these treatments can be recycled without generating scale in process equipment because the solubility of salts that could form such scale is significantly greater in these effluents.

Abstract: A method for reducing or eliminating the formation of salt scale upon process equipment caused by precipitation of insoluble salts during the bleaching of pulp. The pulp is subjected to a bleaching sequence which includes a plurality of pulp treatment steps, wherein at least one pulp treatment step is conducted under alkaline conditions and at least one pulp treatment step is conducted under acidic conditions. A filtrate stream which contains dissolved insoluble salts therein is thus generated, and at least a portion of the filtrate stream is combined with an alkaline stream and pulp to cause the salts to associate with the pulp, thus removing the salts from the filtrate stream to reduce or eliminate the formation of salt scale upon process equipment during the bleaching of the pulp.

Abstract: A process control for adjusting bleaching agent application in response to the pulp brightness and/or K number is realized by utilizing a coupled control feedforward and/or feedback control system or combination thereof wherein brightness measurements are made between successive K number measurements and adjustments made to the bleaching agent application in response to a comparison value.

Abstract: A method for reducing or eliminating the formation of salt scale upon process equipment caused by precipitation of salts during the bleaching of pulp. The pulp is subjected to a bleaching sequence which includes a plurality of pulp treatment steps, wherein at least one pulp treatment step is conducted under alkaline conditions and at least one pulp treatment step is conducted under acidic conditions. A filtrate stream which contains dissolved salts therein is thus generated, and at least a portion of the filtrate stream is combined with an alkaline stream and pulp to cause the salts to associate with the pulp, thus removing the salts from the filtrate stream to reduce or eliminate the formation of salt scale upon process equipment during the bleaching of the pulp.

Abstract: Unbleached pulp is washed with an aqueous alkaline solution in a wash press to substantially uniformly distribute a first amount of alkaline material throughout the pulp. The consistency of the pulp exiting the wash press is above about 18%, preferably between 25 to 35 percent by weight, and the high consistency alkali containing pulp is then treated with oxygen to effect delignification. The use of a wash press reduces the overall amounts of alkaline material utilized in the process compared to processes which add alkaline material to the pulp at low consistency. Additional alkali may be applied, if desired, onto the high consistency pulp prior to oxygen delignification to provide a total amount of between 0.8 and 7 percent by weight of oven dry pulp. High strength, low lignin pulps are formed after oxygen delignification which may be further bleached to high brightness with reduced amounts of bleaching chemicals.

Abstract: An apparatus and method for bleaching high consistency lignocellulosic pulp using ozone supplied in an ozone containing gas. The bleaching reactor apparatus according to the invention is a generally cylindrical vessel itself being rotatable or with a rotatable shaft having radially extending paddles arranged in a configuration to minimize axial dispersion of the pulp and maximize radial dispersion of the pulp to provide a radially dispersed plug flow of pulp through the reactor in the presence of the ozone to provide substantially uniformly bleached pulp.

Abstract: An apparatus and method for bleaching high consistency lignocellulosic pulp using ozone supplied in an ozone containing gas. The bleaching reactor apparatus according to the invention is a generally cylindrical vessel with a rotatable shaft having radially extending paddles arranged in a configuration to minimize axial dispersion of the pulp and maximize radial dispersion of the pulp to provide a radially dispersed plug flow of pulp through the reactor in the presence of the ozone to provide substantially uniformly bleached pulp.

Abstract: A two stage ozone-pulp bleaching method and apparatus are disclosed. In the first stage, high consistency pulp particles are turbulently mixed and contacted with a gaseous mixture containing ozone to mix and contact substantially all of the pulp particles with ozone to react at least a portion of the pulp particles with the ozone. Pulp particles and gaseous bleaching mixture are then directed to a second stage including a quiescent pulp bed. Pulp particles may complete their reaction in the bed, which also serves to strip ozone which was not contacted with pulp particles in the first stage from the gaseous bleaching mixture.

Abstract: A process for delignifying and bleaching a lignocellulosic pulp without the use of elemental chlorine by partially delignifying the pulp to a K No. of about 10 or less and a viscosity of greater than about 13 cps; and further delignifying the partially delignified pulp with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a K No. of about 5 or less, a viscosity of greater than about 10, and a GE brightness of at least about 50%. The substantially delignified pulp may be brightened by the addition of a bleaching agent such as chlorine dioxide or a peroxide to obtain a final product having a GE brightness of at least about 65%, preferably above 70% to as high as 90%. Because of the absence of elemental chlorine in this sequence, filtrate from all stages but the chlorine dioxide stage (if used) can be recovered without sewering. Major environmental improvements are thus achieved.

Abstract: A process for delignifying and bleaching a lignocellulosic pulp without the use of elemental chlorine or chlorine-containing compounds by oxygen delignifying the pulp to a K No. of about 14 or less and a viscosity of greater than about 10 cps and thereafter further delignifying the partially delignified pulp by lifting, displacing and tossing the pulp in a radial direction while advancing it in an axial direction in a plug flow-like manner with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a K No. of about 6 or less, a viscosity of at least about 7 cps and a GE brightness of at least about 35. The substantially delignified pulp may then be brightened to a final product having a GE brightness of at least about 75, or alternately up to about 83 or more by contacting the ozonated pulp with chlorine dioxide or a peroxide compound.

Abstract: A method for controlling the gas recycle loop of an ozone bleaching process wherein an ozone generator produces an ozone containing gas from an oxygen containing feed gas and delivers the ozone containing gas to an ozone reactor at a variable flow rate responsive to reactor ozone demand. Pulp is bleached with the ozone containing gas, thereby producing an exhaust gas having a flow rate that varies in response to the flow rate of the ozone containing gas delivered to the ozone reactor. The exhaust gas is then recovered and its flow rate is modified within the recycle loop so that an amount equivalent to reactor ozone demand is returned to the ozone generators. The oxygen content of the oxygen containing feed gas is monitored at or near the inlet of the ozone generator and an amount of fresh oxygen is supplied to the oxygen containing feed gas to obtain a predetermined level of oxygen therein.

Abstract: Unbleached pulp is combined with an aqueous alkaline solution while in a state of low consistency to distribute a first amount of alkaline material substantially uniformly throughout the pulp. The consistency of the pulp is then increased to above about 18%, and the high consistency alkali containing pulp is then treated with oxygen to effect delignification. The total amount of alkaline material applied to the pulp is between 0.8 and 7% by weight of oven dry pulp. High strength, low lignin pulps are subsequently formed which may be further bleached to high brightness with reduced amounts of chemicals.

Abstract: A process for delignifying and bleaching a lignocellulosic pulp without the use of elemental chlorine by partially delignifying the pulp to a K No. of about 10 or less and a viscosity of greater than about 13 cps; and further delignifying the partially delignified pulp with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a K No. of about 5 or less, a viscosity of greater than about 10, and a GE brightness of at least about 50%. The substantially delignified pulp may be brightened by the addition of a bleaching agent such as chlorine dioxide or a peroxide to obtain a final product having a GE brightness of at least about 65%, preferably above 70% to as high as 90%. Because of the absence of elemental chlorine in this sequence, filtrate from all stages but the chlorine dioxide stage (if used) can be recovered without sewering. Major environmental improvements are thus achieved.

Abstract: A process for delignifying and bleaching a lignocellulosic pulp without the use of elemental chlorine by partially delignifying the pulp to a K No. of about 10 or less and a viscosity of greater than about 13 cps; and further delignifying the partially delignified pulp with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a K No. of about 5 or less, a viscosity of greater than about 10, and a GE brightness of at least about 50%. The substantially delignified pulp may be brightened by the addition of a bleaching agent such as chlorine dioxide or a peroxide to obtain a final product having a GE brightness of at least about 65%, preferably above 70% to as high as 90%. Because of the absence of elemental chlorine in this sequence, filtrate from all stages but the chlorine dioxide stage (if used) can be recovered without sewering. Major environmental improvements are thus achieved.