Emerging Biodrying Technology for the Drying of Pulp and Paper Mixed Sludges

Effective sludge management is increasingly critical for pulp and paper mills due to high landfill costs and complex regulatory frameworks for options such as sludge landspreading and composting. Sludge dewatering challenges are exacerbated at many mills due to improved in-plant fiber recovery coupled with increased production of secondary sludge, leading to a mixed sludge with a high proportion of biological matter that is difficult to dewater. Various drying technologies have emerged to address this challenge of sludge management, whose objective is to increase the dryness of mixed sludge to above critical levels (≈42% dryness) for efficient and economic combustion in the boiler for steam generation. The advantages and disadvantages of these technologies are reviewed in this article, and it is found that many have significant technical uncertainties and/or questionable economics. A biodrying process, enhanced by biological heat generation under forced aeration, is introduced that has significant promise. A techno-economic analysis of the batch biodrying process at a case study mill showed an annual operating cost savings of about $2 million, including the elimination of landfilling practices and supplemental fuel requirements in the boiler. It was shown that if a biodrying residence time of less than 4 days can be achieved, payback periods of 2 years or less can result in many mills. The potential for the development of a continuous biodrying reactor and the fundamentals of its mathematical modeling are thus presented. Compared to the batch reactor configuration, it is expected that the continuous process would result in improved process flexibility and controllability, lower investment and operating costs due to shorter residence times, and an improved potential to fit into the crowed pulp and paper mill site.     

Developments in Ozone-Based Bleaching of Pulps

ABSTRACT

This paper summarizes the review of developments in the area of ozone-based elemental chlorine free (ECF) and total chlorine free (TCF) bleaching of wood and non-wood pulps. Focused areas of review are reaction mechanism of ozone with carbohydrates and lignin, effect of process conditions maintained during ozone bleaching on pulp properties, effect of using different cellulose protectors, effect of alkaline extraction after ozone bleaching of pulps, effect of ozone bleaching on final bleached pulp properties, ECF and TCF bleaching sequences used along with ozone for of wood and non-wood pulps, and commercial scale utilization of ozone for pulp bleaching.     

Wastewater Minimization in Pulp and Paper Industries through Energy‐Efficient Reverse‐Osmosis Membrane Processes

Fresh water consumption and wastewater management is a mandatory task to conserve water resources and to reduce wastewater discharge from chemical production processes. Such objectives have been addressed in many industrial sectors which consume large amounts of fresh water. Possibilities for reducing wastewater volumes by regeneration and recycling routes in the pulp and paper industry are analyzed. During pulp preparation and paper making processes by the Kraft pulping method a large amount of water is required to deliver the finished paper product. Reverse osmosis (RO) is applied for the analyses as an interception separation technology to reduce salt concentrations in wastewater streams for recycling purposes. The RO network synthesis problem is formulated as mixed integer nonlinear programming model which is solved using the general algebraic modeling system. A preliminary cost estimate indicates economic incentives by installation of RO units to avoid wastewater discharge and generate relatively clean water streams for inter‐plant usage.     

TREATMENT OF KRAFT PULP AND PAPER WASTEWATERS BY MEANS OF FOAM SEPARATION

The pulp and paper industry is the third largest industrial consumer of fresh water in the United States. The current use rate of over two trillion gallons annually is expected to increase as the demand for paper products continues to rise

Of the various methods of producing paper from wood, the Kraft process is the most widely used. Color, dissolved and suspended organic matter, and dissolved inorganic solids are major pollutants in Kraft processing wastewater. Current federal regulations limit the amount of solids and organic matter that a Kraft facility may dispose into public waters, so most plants have some form of wastewater treatment

In this study, the capacity of a continuous-flow, foam separation system to effect removals of color from a Kraft process wastewater was evaluated. The cationic surfactant, EHDABr, was used to precipitate color bodies in the wastewater and create a foam to carry the precipitates from the wastewater. The effect of pH adjustment was also considered. Color removals in the area of 90% were achieved

Removal of precipitated solids was enhanced by increasing the detention of wastewater in the treatment system.     

Degradation of Cellulose Models During an Ozone Treatment. Ozonation of Glucose and Cellobiose With Oxygen or Nitrogen as Carrier Gas at Different pH

Many parameters can influence the kinetics of cellulose models ozonation. In this work the effect of pH and oxygen as gas carrier on the evolution of the reaction was studied. The involvement of free radical species seemed to be unimportant in high ozone concentration available in water, even at high pH with regard to the reaction rate and by-product formation. Conversely, in basic pH conditions better reaction selectivity with formation in a higher yield of gluconic acid and cellobionic acid was found during the glucose and the cellobiose ozonation. The participation of the solvent and the partial ionization of the hydroxyl group at the Cl position explain this enhanced selectivity. Furthermore, the formation of compounds with a low molecular weight has been proved to be due to a hydrotrioxide fragmentation mechanism involving oxygen.     

一种流态化筛分设备的研制与试验研究

流态化立式筛分设备通过完全不同于常规筛分设备的结构形式和给料方式,解决了普通筛分设备易堵塞的问题,比普通振动筛具有更好的可操作性,对矿浆浓度和矿石粒度组成具有较强的适应性,筛分效率高,指标稳定可靠.流态化立式筛分设备筛网使用寿命明显高于相同材质筛网的普通筛分设备,通过逆向给料和脉动系统解决了普通筛分设备易堵塞与寿命短的...     

对氨基苯酚对硫化矿物的抑制性能及电化学机理研究

本文研究了矿浆电位对有机药剂对氨基苯酚抑制性能的影响以及对氨基苯酚与硫化矿物作用的电化学机理。研究结果表明矿浆电位能够影响对氨基苯酚的抑制活性 ,控制对氨基苯酚的用量、矿浆pH以及矿浆电位可以实现多种硫化矿物的分离。对氨基苯酚与硫化矿物的作用机理不是静电作用而是电化学作用 ,对氨基苯酚能够降低硫化矿物的边缘能级 ,增加矿物表面电子密度 ,从而降低矿物表面捕收剂膜的稳定性     

光折变的光学脉动现象及其非线性过程

报道了光折变LiNbO_3:Fe晶体中双光束耦合和四波混频的脉动现象。认为这种脉动现象起因于LiNbO_3:Fe晶体中的陷阱重复荷电波在光折变材料中感应出的运动折射率光栅。