Energy efficiency in low consistency refining: a study using a Valley beater

The purpose of this work was to study the influence of pulp fiber suspensions refining operating variables on energy efficiency coefficient. Three chemical pulps with different average morphological characteristics were used, obtained from bleached kraft Pinus sylvestris, Eucalyptus globulus and Betula verrucosa. The final objective was to establish the chemical pulps refining efficiency parameters. Refining hydromechanics and energy consumption profiles were analyzed. Average normal and tangential forces on pulp suspension in the gap clearance, resulting rotor-stator distance and no-load and refining conditions power consumption were obtained. The refining trials took place in a laboratory Valley beater, and the manipulated variables were charge on the roll and rotor rotation speed. Global relationships for tangential stress and energy efficiencies in terms of rotation speed and rotor-stator gap were obtained. A relationship between energy efficiency and shear stress was obtained. The results have shown that in a Valley beater increased rotor-stator gaps reduce energy efficiency, concomitantly increasing apparent viscosity and reducing shear stress. No-load power was seen to increase with crowding factor, and thus with flocculation. Inversely, crowding factor and ultimately flocculation had an adverse effect on energy efficiency.

Through air drying assisted by infrared radiation: the influence of radiator power on drying rates and temperature

The use of infrared radiation for heating the web in the through air drying process was investigated in lab scale. The hypothesis was that infrared radiation should be a more efficient method to transfer drying energy to the wet web compared to hot air, but that a certain air flow is still required as a transport medium for the evaporated water. A trial program comprising handsheets made of two types of bleached chemical pulps, five grammages (15, 22, 30 and 60 g/m²), and dried with five radiator power levels was performed on a lab scale through air drying equipment. Drying times of the samples were determined from temperature data recorded with an infrared camera. The use of infrared radiation shortened drying times, especially for low grammage samples. The shortening of the drying time ranged between 10 and 45 %. The most substantial shortenings were obtained for the lowest grammages and the highest radiator power level. However, the increase of power did not linearly shorten drying time. After an initial shortening at the lowest power level, the positive effect of the IR heating decreased as the power was further increased.

Eco-Friendly Bleaching of Soda-AQ Chemical Elephant Dung Pulp

<div><p><em>Elephant dung is an excellent source of cellulosic fibers that is a basic requirement for paper making. In this study, bleaching was carried out by using eco-friendly bleaching agents such as sodium percarbonate, oxone and hydrogen peroxide. Soda-anthraquinone (soda-AQ) semi-chemical and chemical elephant dung pulps were bleached at varying doses of bleaching agents, bleaching aids and reaction time. Presence of residual lignin after pulping stage was imparting brown color to the pulp and hence was removed by subsequent bleaching stages. Soda-AQ chemical pulps was treated with different multistage bleaching sequences. The results of this study showed that sodium percarbonate and oxone could not achieve targeted brightness for elephant dung pulp samples. Whereas, using three stage hydrogen peroxide bleaching sequence [AP₅P₃P₂] helped to achieve the targeted brightness ~ 60.0 % G.E without much sacrificing the other optical and physical properties of the pulp. Eco-friendly bleaching helped to increase the beauty of the final product. Being rich in fiber, elephant dung pulp has a potential to be blended with other raw materials to make hybrid exotic papers of high market value.<strong></strong></em></p></div>

New evidence for the role of the borohydride pretreatment on the hydrogen peroxide bleaching of kraft pulp

New evidences for the role of borohydride pretreatment in hydrogen peroxide bleaching process of eucalyptus chemical pulps were provided, i.e., suppressing the catalysis effect of Fe(iii), decreasing carbonyl groups, and constituent lignin structure.

Influence of cellulose supramolecular structure on strength properties of chemical pulp

The industrially produced chemical pulps have lower strength properties than those obtained under laboratory conditions, and this difference is referred to as the strength delivery (SD) problem. In this study, the hypothesis was put forward that the SD could, at least in part, be accounted for by the supramolecular structure of the cellulose microfibrils of the fiber wall. To test the hypothesis, two bleached softwood kraft pulps (BSKP) were manufactured from the same starting material with different degrees of cellulose aggregation, but the pulps were otherwise as similar as possible in other controllable respects. The chemical and physical properties, including the pulp strength, were tested. A selective increase of the degree of cellulose microfibril aggregation resulted in a pulp with a decreased tear index (TI) at a specified tensile index, and this decrease was similar in magnitude to what is typically encountered in SD. Accordingly, the current experimental study succeeded in mimicking the SD problem. The lateral fibril aggregate dimensions (LFAD) seem to play a pivotal role and it can be safely concluded in general that the supramolecular structure of cellulose in the fibers may be an important factor contributing to the SD problem.

Recycling potential of unbleached and bleached chemical pulps from juvenile and mature wood of Populus deltoides

The recycling potential of unbleached and bleached pulps of juvenile and mature wood of poplar (namely “eastern cottonwood”, Populus deltoides) has been investigated. First, chemical and morphological characteristics of juvenile wood (JW), transition wood, and mature wood (MW) of the trunk were determined. Then, high yield and low yield pulps were produced separately from JW and MW by kraft pulping (KP), followed by bleaching of the low-yield pulp with a DED sequence. The obtained handsheet papers were subjected to five successive drying and rewetting cycles (as recycling simulation), and the properties of the corresponding pulps were characterized. The results show that JW is inferior with respect to chemical and morphological properties and resulted in low-yield KP. The bleached pulp obtained from JW required more bleaching chemical to achieve the brightness targets. The strength losses of pulps resulting from recycling were more significant in the first recycling cycle, and then the loss rate decreased with further cycles. The comparison between different pulps showed that the JW pulps were more susceptible to the effects of recycling than MW pulps.