摘要:
In the mechanical refining of wood chips to produce wood pulp, wood pulp quality is improved by employing low refining intensity at least in a final refining stage; the refining is carried out in a double disc refiner or a single disc refiner at rotational speeds that are lower than those conventionally employed, specifically at less than 1200 RPM in a double disc refiner and at less than 1500 RPM in a single disc refiner.
摘要:
A rapid method is provided for the on-line spectroscopic determination of lignin content and/or kappa number in wood pulps. Unlike currently available commercial instrumentation, the method enables one to measure lignin content independently of species variations and pulp consistency. The method includes the steps of: (1) withdrawing high-consistency samples of wood pulp from a chemical pulp manufacturing process; (2) subjecting these samples to a monochromatic visible-light source; (3) recording the resulting scattered light and its Raman spectrum over a predetermined range of wave numbers so as to produce Raman-scattered light intensity measurements; (4) determining either the uncorrected, baseline-corrected and/or integrated Raman-scattered light intensity of the samples over a predetermined range of wavenumbers shown by different combinations of lignin content, cellulose content, and consistency; (5) correlating by either univariate or multivariate calibration the relationships between the Raman-scattered light intensity measurements of unknown samples and the Raman-scattered light intensity shown by known combinations of lignin content, cellulose content, and consistency so that the lignin content and/or kappa number in wood pulps can be accurately determined over a Kappa range of 5 to 110 and preferably 5 to 20, for any levels of sample cellulose content or pulp consistency.
摘要:
A method for determining the concentration of hydrogen ion, organic anionic species and anionic species selected from the group consisting of OH-, CO3?=, HS-, ClO¿3-, SO4=, S2O3=, polysulphide and peroxide in an aqueous sample solution, said method comprising subjecting said solution to near infrared radiation at a wavelength region of wave numbers selected from about 7,000 to 14,000 cm-1 through a solution path length of at least 3 mm to obtain spectral data for said solution; obtaining comparative spectral data for said anionic species at known concentrations in aqueous solutions; and correlating by multivariate calibration the relationships between said spectral data of said sample solution and said comparative spectral data to determine said concentration of said anionic species in said sample solution. The method is of particular value for use with pulp liquor determination and control.
摘要:
Solid films with novel optical properties are produced from colloidal suspensions of cellulose crystallites; the colloidal suspensions are prepared by acid hydrolysis of crystalline cellulose under carefully controlled conditions; the solid materials possess a helicoidal arrangement of the constituent crystallites; by appropriate selection of conditions for preparation and treatment of the colloidal suspensions, solid films are produced that reflect circularly polarized visible light; the wavelength of the reflected light can be controlled to give colours across the visible spectrum from red to violet, and if necessary to infrared and ultraviolet wavelengths. The reflected iridescent colours arise from optical interference effects, and change with the viewing angle; this makes the materials ideally suited for optical authenticating devices, since no printing or photocopying technique can reproduce this effect; furthermore, they are easily distinguishable from other optical interference devices since thay have additional optical properties.
摘要:
A process employing a fixed-resin bed Acid Retardation Unit (ARU) to separate spent acid from chlorine dioxide generators into a de-acidified sodium sulfate component and a purified sulfuric acid component. The de-acidified sodium sulfate produced is returned to the chemical recovery cycle of the kraft mill in place of acidic chlorine dioxide generator effluent thereby avoiding the destruction of alkalinity in pulp mill liquors. In addition, sulfuric acid is purified providing an opportunity for reuse in various mill applications, and/or concentrated and recycled to the generator. Alternatively, to avoid high evaporation costs, the purified acid can be used to regenerate a cation-exchange unit (CEU) used in the conversion of sodium chlorate to a sodium chlorate/chloric acid mixture which is fed to the generator in place of sodium chlorate and sulfuric acid. Using this approach, the sulfuric acid requirement of chlorine dioxide generators and, in turn, the amount of acidic generator effluent can be reduced. The process is applicable to both atmospheric and subatmospheric chlorine dioxide generators. In the latter case, the concentration of the purified sulfuric acid from the ARU or any other acid separation system can be increased by using a portion of it to dissolve the sodium sesquisulfate by-product from such generators.
摘要:
A method of diagnosing a malfunction of a process control system which includes at least one closed loop control loop comprising measuring a histogram of tracking error of the control loop, determining distortion of the tracking error relative to a Gaussian distribution, and indicating a malfunction in the process in the event a deviation from the Gaussian distribution of the tracking error exceeds predetermined limits.
摘要:
A rapid method is provided for the on-line determination of sodium sulfide concentration and/or percent sulfidity in green liquors or smelt solutions used for the production of either kraft or sulfite pulp. The method eliminates manual sampling, and the need for frequent equipment maintenance. The method includes the steps of withdrawing samples of a smelt solution or green liquor from the kraft or sulfite manufacturing process, subjecting the samples to near-infrared spectrophotometry over a predetermined range of wave numbers so as to produce absorbance measurements relative to a reference spectrum of either water or a caustic soda-sodium carbonate solution, determining the absorbance shown by different combinations of sodium sulfide, sodium hydroxide, sodium carbonate and sodium chloride concentrations, correlating by multivariate calibration the relationships between the absorbance measurements of unknown samples and the absorbance shown by different combinations of sodium sulfide, sodium hydroxide, sodium carbonate and sodium chloride so that the amount of sodium sulfide and/or the percent sulfidity can be accurately determined for any levels of TTA or chloride present in the liquor.
摘要:
A method for bleaching cellulosic and lignocellulosic pulp using hydrogen peroxide as a bleaching reagent, utilizes a two-step reaction, viz. a short high temperature step at a pressure sufficient to suppress boiling and a longer atmospheric pressure reduced temperature step to consume a substantial portion of the hydrogen peroxide remaining after the short phase. The method includes the steps of introducing pulp (15), at a consistency of 10 %-18 %, to a mixer (100) in which the pulp is heated to a temperature above 100 °C; adding sufficient sodium hydroxide to bring the pulp to a pH of 8.5; adding sufficient hydrogen peroxide (36) to equal from about 0.5 %-5.0 %, by weight, of the pulp; passing the pulp through a pressurized reactor column (400) at a rate providing a reaction time in the column of between 1 and 30 minutes; and depositing the pulp in a reaction tower and allowing the reaction to proceed for 1-5 hours until a substantial portion of the residual hydrogen peroxide has been consumed. It may be desirable to introduce the pulp to a mixer and add alkali to reactivate residual hydrogen peroxide by bringing the pulp to a pH of at least 9 between bleaching steps.