Showing papers in "Appita Journal in 2012"

Comparison of mechanical pulps from two stage HC single disc and HC double disc - LC refining

Abstract: A mechanical pulping line consisting of high consistency (HC) double disc (DD) and low consistency (LC) refining was compared with a two stage single disc (SD) high consistency twin refiner line. The purpose of this study was to evaluate specific energy consumption and pulp properties. The two different process solutions were tested running similar Norway spruce wood supply. At similar tensile index and freeness, the DD-LC concept reduced the electric energy consumption by 400 kWh/adt compared with the traditional two-stage SD-SD system. Pulp characteristics of the two refining concepts were compared at tensile index 47 Nm/g. Fibre length was reduced more after DD-LC refining than after SD-SD refining. Specific light scattering coefficient was higher after DD-LC refining than SD-SD refining, while the development in second stage refining was better for SD-SD pulp than for DD-LC pulp. Shive level was significantly lower for DD-LC pulp than for SD-SD pulp.

Process factors affecting colloid stability and deposit formation in manufacture of newsprint from TMP and recycled fibre

Abstract: SUMMARY Formation of pitch and sticky deposits through the destabilisation of colloidal material present in paper manufacture continues to be a challenge in improving machine efficiency in newsprint manufacture from a furnish comprising thermo-mechanical pulp (TMP) and recycled fibre (RCF), and in an environment where water usage efficiency is at best practice. Findings from laboratory studies that have investigated colloid structure, impact of multiple and multi-valent cations, pH, temperature, shear and dissolved organic matter on Pinus radiata extractive colloid stability have been used , along with observations of process conditions in Norske Skog’s Albury mill to determine which properties are most important in maintaining colloid stability. Developments in our understanding of wood extractive colloid structure have led to an explanation as to why pitch deposition is more likely during summer months. A parameter called the “ester to acid ratio” has been shown to exhibit both short and long-term trends when applied to process stream extractive levels. This greater propensity for deposition during summer months is exacerbated by elevated soluble calcium levels during summer time. Dissolved organic wood polymers also affect colloid stability and their behaviour is further modified by the presence of soluble calcium. More stable colloids are obtained under conditions of neutral pH, avoidance of downward temperature shocks and avoidance of shear forces.

Addition of trace metals and vitamins for the optimisation of a pulp and paper mill activated sludge wastewater treatment plant

Abstract: Generally, industrial wastewater does not contain sufficient micronutrients to support optimal bacterial growth as a number of micronutrients are essential for biological cell function and activated sludge stability. A laboratory scale activated sludge process using porous pots with a capacity of 4.5 L has been used to mimic the operation of an activated sludge plant. Water soluble B group vitamins and trace metals including calcium, cobalt, copper, iron, magnesium, molybdenum and zinc were chosen for the micronutrient addition trials. The results indicated that COD removal was significantly improved by 7 to 12% compared to a control by the addition of calcium, cobalt, copper, iron and magnesium.

Is the Australian pulp and paper industry still at the crossroads

Abstract: In 2010, an article was published in Appita Journal setting the scene of the forest sector in Australasia at that time (4). How has the situation changed and how can the future success in terms of improved value appropriation by the industry be seen? Is the future in conventional paper and board making or is there a future that incorporates the existing technologies together with biorefineries of various forms as well as other emerging biomass opportunities? Countless authors world-wide have indicated that there are many factors driving the demand and markets for new biomass products such as biofuels, biochemicals and other renewable products. Among these factors is the exponential growth in the global population, the need to mitigate climate change, as well as to reduce dependency on increasingly expensive oil and to improve the security of energy supplies. Value for money, cost competitiveness and environmental sustainability will be key issues in future markets for biomass-based products. Integrated production in large biorefineries will create cost advantage and competitiveness, whereas innovation will provide the basis for value for money. Small, distributed biorefineries may also become important in future development phases. The existing know-how at VTT is a basis for creating new businesses and new products from biomass. Biorefineries can use biomass raw materials from various sources: forest-based biomass, agrobiomass and various waste and side streams. Identifying new value chains and profit pools are essential. Cooperation between companies from different industrial clusters is needed for successful innovations based on biomass. The implications for the future local forest sector will be discussed for the following scenarios (1) maintain the status quo, (2) off shore resource ownership, and (3) retain benefits through new technology enhanced value chains.

Selective froth flotation of pitch components from spruce TMP process water

Abstract: Selective removal of dissolved and colloidal pitch components from an unbleached thermomechanical pulp (TMP) pressate by addition of a cationic foaming agent, dodecyltrimethylammonium chloride (DoTAC), and subsequent froth flotation was assessed. The experiments were conducted with varying pH, temperature, and concentrations of DoTAC and calcium. The concentrations of pitch components, lignans, and dissolved polysaccharides were determined before and after flotation. All pitch components were removed more efficiently by flotation at pH 5 and 3.5 than by flotation at pH 7.6. Resin and fatty acids were removed to a higher degree than neutral pitch substances at all the tested pH levels. Most of the water-soluble uronic acids and galactoglucomannans stayed in the TMP water after flotation. Froth flotation with DoTAC was an effective way of selectively removing colloidal and dissolved pitch. Removal of pitch, especially of resin acids, at an early stage should be beneficial to the overall papermaking process.

Effect of increased levels of dissolved and colloidal substances from Pinus radiata on newsprint paper strength

Abstract: The effect of increased levels of wood resins, salts and dissolved organics on newsprint tensile strength was evaluated. Significantly more Pinus radiata wood resins are adsorbed onto the fibre surface compared to reported results for Norwegian spruce. Differences in chemical composition may explain this. Tensile strength was found to decrease significantly and reach a limiting value as the level of wood resins in the handsheets increased to approximately 5 mg/g acetone extractives. High levels of calcium ions were found to cause precipitation of the wood resins onto the fibre surface and also reduced tensile strength. Increasing amounts of soluble polysaccharides, such as galactoglucomannans, were found to stabilize the wood resins in solution and reduce the amount adsorbed onto the fibre surface, resulting in increased tensile strength. The addition of polymeric fixatives was found to reduce the negative effect of the higher levels of extractives attached to the fibres.