造纸废水处理工艺的应用

论述了造纸厂废水不同的处理工艺及其特点.对比了各种不同的处理工艺得到以下结论:厌氧和好氧工艺的结合能有效去除可溶性可生物降解的有机污染物;通过真菌处理、絮凝、化学法、臭氧处理可以有效去除色度等;通过吸附、臭氧处理和膜过滤技术可有效去除含氯酚类有机物以及可溶性有机卤化物等.     

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.     

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.     

Energy system diagnosis of paper-drying process,Part 1: Energy performance assessment

Paper drying is a highly energy-intensive and complicated multivariate process. The dryer section plays an important role in the energy consumption of a paper machine, especially of thermal energy. A comprehensive method for assessing the energy performance of the dryer section was investigated in this study to improve energy efficiency. This method was divided into three component processes: energy and evaporation load audit, field test and observation, and energy flow analysis and energy efficiency estimation. In a case study, we found that the method could, in addition to analyzing the key factors that restrict drying efficiency, also depict the details of energy consumption clearly. At the same time, several significant energy-saving measures were suggested to improve the energy efficiency of the paper-drying process.     

Membrane evaluation for the treatment of acidic clear filtrate

The total effluent load of a paper mill can be significantly decreased by recycling of purified clear filtrate (CF) back to paper-making process. The CF treated with membranes can be reused, for instance, as wire section shower water and in the dilution of chemicals. The main requirements for a membrane in CF treatment are high filtration capacity, high retention of turbidity and low fouling tendency. Previous studies have shown that the regenerated cellulose (RC) ultrafiltration (UF) membrane C30F (current trade name UC030T) is especially suitable for the treatment of paper mill process waters. Every paper-making process is, however, different. Thus, filtration experiments are required in order to find the most optimal membrane for the treatment of a certain process water. In this study the best membrane for the treatment of acidic clear filtrate (ACF) was searched. The performance of the C30F membrane was compared with five UF and three microfiltration (MF) membranes. The results revealed that in addition to the C30F membrane, also some other membranes produced high filtration capacity with ACF (approximately 200 L/(m²h bar)). All the tested membranes also retained over 90% of turbidity. The extremely hydrophilic C30F membrane had, however, lower fouling tendency compared to the other tested membranes. Therefore, it was concluded that the C30F membranes were the best possible membrane for the ACF treatment.     

Drying of Activated Sludge Under Partial Vacuum Conditions—An Experimental Study

A typical wastewater treatment system in a pulp and paper mill in Finland treats wastewater both mechanically and biologically. Sludges resulting from these processes have to be disposed of. One possible way of doing this is to incinerate them with solid fuel in the power plant of the mill. To minimize the amount of sludge and to make the use of the sludge energy efficient, it has to be dried before incineration. Mechanical drying of the sludge from biological wastewater treatment is difficult to carry out. Using secondary energies may provide a competitive way of arranging drying: a method of doing this by using partial vacuum evaporation to utilize the low temperature secondary heat in sludge drying is under development. A laboratory study to examine the behavior of activated sludge under partial vacuum evaporation conditions was carried out using a laboratory rotating evaporator to analyze the drying of activated sludge from three mills at 40-80°C boiling temperatures. This article presents the results from the tests. These are promising; it was possible to reach high dry solids content. Also, no boiling point temperature rise was detected, fouling of the evaporator seemed low and easily avoidable, condensate from the evaporator weas relatively clean and returnable to the processes of the mill.     

Reduction of chlorophenols and sludge management from paper industry wastewater using electrocoagulation process

ABSTRACT

In this study, electrocoagulation (EC) was used to determine the optimum conditions on the basis of maximum chemical oxygen demand (COD) and color removal. At the optimum conditions chlorophenols (CPs), biological oxygen demand and total organic carbon (TOC) were determined. The biodegradability of wastewater was increased significantly with 63% COD, 98% color, 61% TOC and overall 65.51% reductions in CPs. Further, the electro-coagulated sludge was characterized by using different analytical techniques to assist the physicochemical and elemental phases, to find-out better management option, reusability for plant growth and safe disposal. Additionally, aluminum content (70.62%) was successfully recovered from sludge.     

Drying of Activated Sludge Under Partial Vacuum Conditions—An Experimental Study

Abstract

A typical wastewater treatment system in a pulp and paper mill in Finland treats wastewater both mechanically and biologically. Sludges resulting from these processes have to be disposed of. One possible way of doing this is to incinerate them with solid fuel in the power plant of the mill. To minimize the amount of sludge and to make the use of the sludge energy efficient, it has to be dried before incineration. Mechanical drying of the sludge from biological wastewater treatment is difficult to carry out. Using secondary energies may provide a competitive way of arranging drying: a method of doing this by using partial vacuum evaporation to utilize the low temperature secondary heat in sludge drying is under development. A laboratory study to examine the behavior of activated sludge under partial vacuum evaporation conditions was carried out using a laboratory rotating evaporator to analyze the drying of activated sludge from three mills at 40–80°C boiling temperatures. This article presents the results from the tests. These are promising; it was possible to reach high dry solids content. Also, no boiling point temperature rise was detected, fouling of the evaporator seemed low and easily avoidable, condensate from the evaporator weas relatively clean and returnable to the processes of the mill.     

Energy Efficiency and Drying Kinetics of Recycled Paper Pulp

In this work, the influences of the air temperature and velocity on the drying kinetics of recycled paper pulp were analyzed. The increase of both variables positively influences the process, concerning the final moisture content and the drying time. However, optical microscopy and visual observation showed worse quality of the paper for drying conditions of high air temperature and velocity, presenting less uniformity and overdried surfaces. The dryer energy efficiency was evaluated by performance parameters and the results were compared with the ones obtained for other types of industrial paper dryers, presenting good agreement.     

Energy Efficiency and Drying Kinetics of Recycled Paper Pulp

In this work, the influences of the air temperature and velocity on the drying kinetics of recycled paper pulp were analyzed. The increase of both variables positively influences the process, concerning the final moisture content and the drying time. However, optical microscopy and visual observation showed worse quality of the paper for drying conditions of high air temperature and velocity, presenting less uniformity and overdried surfaces. The dryer energy efficiency was evaluated by performance parameters and the results were compared with the ones obtained for other types of industrial paper dryers, presenting good agreement.     

Energy system diagnosis of paper-drying process,Part 2: A model-based estimation of energy-saving potentials

The pulp and paper sector is the fourth largest industrial sector in terms of energy use in the world. Of the numerous processes involved in paper-making by a paper machine, the dryer section is the process that consumes the largest amount of energy. A model-based method for estimating energy-saving potentials of the dryer section was put forward in the present study. It was done by four steps: establishing a mathematical model about energy consumption, determining the model parameters, benchmarking the drying performance to obtain the corresponding energy-saving measures, and estimating the energy-saving potentials by using the mathematical model. In a case study, a multi-cylinder dryer section was selected to illustrate the method. After a fundamental field test and observation, several operating problems that restricted the energy performance of paper drying were found. And then several reasonable energy-saving measures were suggested to the operators. Finally, applying the mathematic model, it was found that 0.32 ton of steam will be saved when producing 1 ton of paper in recommended operating conditions. With the designed capacity of 200,000 tons/year, the annual steam-savings will be 64,000 tons. Generally, the price of steam is 130–150 Chinese Yuan (about US$21–24) in China, and the annual economic benefits will be 8.32–9.60 million Chinese Yuan (about US$1.344–1.536 million).     

A CASE STUDY FOR CONTROL STRUCTURE SELECTION: CHLORINATION STAGE IN THE BLEACHING PROCESS OF A PULP AND PAPER PLANT

The minimization of chlorinated organic compounds in the effluents of the chlorination unit of a pulp mill is proposed by the use of a control structure for the chlorination unit. Bleached pulp properties are related to the unbleached pulp properties: lignin content, brightness, and viscosity, as well as the amount of chlorinated organics in the bleachery effluent. The best feasible control pairings are studied by RGA and SVD methods. Kappa number of the bleached pulp (a measure of lignin content) and percent consistency of the pulp to be bleached; residual chlorine (which affects the amount of chlorinated organics discharged) and percent chlorine/pulp ratio adapted in the chlorination stage; and exit pulp viscosity (which directly affects strength and tear resistance of the paper) and residence time in the chlorinator are chosen to be the best pairings.     

Iterative optimization of the economic efficiency of an industrial process within the validity area of the static plant model and its application to a Pulp Mill

Optimization of the steady state economic efficiency of an industrial process is a specific task because the decision variables of the optimization (setpoints of the control system) affect the process through the control strategy. Thus, the effects of saturation of a control system must be taken into account when the gradient of the objective function is estimated and the necessary optimality conditions are checked. In particular, because the optimality conditions cannot be checked directly in the presence of active constraints on the manipulated variables, approximations of the steady state values of the manipulated variables as functions of the setpoints (static plant model) are needed in order to be able to evaluate the optimality conditions. In this paper an iterative method for optimization of the plant profit rate is proposed avoiding the control saturation and is applied to the Pulp Mill benchmark model optimization. Three different static models describing the steady state values of the manipulated variables are constructed and used in the optimization. The results of the optimization are presented and compared against the straightforward single-step optimization of the plant economic efficiency.     

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.     

A Modular Process Modeling Tool for the Analysis of Energy Use and Cost in the Pulp and Paper Industry

A novel process modeling tool to facilitate the study of how various process changes in the paper dryer section affect the mill-wide energy system has been developed. A model library with steady-state block models describing paper dryers, heat recovery equipment, and auxiliary systems on component level have been developed using the software Extend. Process models are then created from these block models using graphical programming. In this article, the characteristics of the developed tool are described and a case study where the tool is shown to be useful for analyzing the energy performance of a hybrid dryer section is presented.     

A Modular Process Modeling Tool for the Analysis of Energy Use and Cost in the Pulp and Paper Industry

A novel process modeling tool to facilitate the study of how various process changes in the paper dryer section affect the mill-wide energy system has been developed. A model library with steady-state block models describing paper dryers, heat recovery equipment, and auxiliary systems on component level have been developed using the software Extend. Process models are then created from these block models using graphical programming. In this article, the characteristics of the developed tool are described and a case study where the tool is shown to be useful for analyzing the energy performance of a hybrid dryer section is presented.     

Post-Treatment of Pulp and Paper Industry Wastewater by Advanced Oxidation Processes

The aim of this study was to investigate the effectiveness of chemical oxidation by applying ozonation, combination of ozone and hydrogen peroxide and Fenton's processes for decolorization and residual chemical oxygen demand (COD) removal of biologically pretreated pulp and paper industry effluents. The batch tests were performed to determine the optimum operating conditions including pH, O₃, H₂O_2, and Fe²⁺ dosages. H₂O₂ addition reduced the reaction times for the same ozone dosages; however combinations of ozone/hydrogen peroxide were only faintly more effective than ozone alone for COD and color removals. In the Fenton‘s oxidation studies, the removal efficiencies of COD, color and ultraviolet absorbance at 254 nm (UV₂₅₄) for biologically treated pulp and paper industry effluents were found to be about 83, 95, and 89%, respectively. Experimental studies indicated that Fenton oxidation was a more effective process for the reduction of COD, color, and UV₂₅₄when compared to ozonation and ozone/hydrogen peroxide combination. Fenton oxidation was found to have less operating cost for color removal from wastewater per cubic meter than the cost for ozone and ozone/hydrogen peroxide applications.     

山东省造纸工业发展中建设项目环境管理简析

阐述了当前山东省造纸产业发展状况,通过加强流域治理,加强项目管理机制,开展环评规划,提高环境入门槛等方面对山东省造纸工业发展中建设项目环境管理进行简析,希望对造纸工业的发展起到一个建议性的思路.     

Stepwise Development of a Mathematical Model for Air Flow in Vacuum Dewatering of Paper

Part of the dewatering in a paper machine takes place via vacuum suction boxes situated below the moving web. In addition to the removal of liquid water, considerable amounts of air are sucked through the paper. The air flow that accompanies dewatering is a crucial parameter for the electricity consumption of a vacuum system. The present study models this air flow, combining differential conservation equations with fiber characterization. Measured air flow rates for different vacuum levels, basis weights, and pulp types are compared to model predictions. More than 70% of the data agree within the range of experimental error.