Đề tài Cleaner production audit in the pulp and paper industry: a case study in vietnam

CLEANER PRODUCTION AUDIT IN THE PULP AND PAPER INDUSTRY: A CASE STUDY IN VIETNAM by Vu Tuong Anh A thesis submitted in partial fulfillment of the requirement for the degree of Master of Science Examination Committee : Dr. C. Visvanathan (Chairman) Mrs. Samorn Muttamara Dr. Nguyen Thi Kim Oanh Vu Tuong Anh Nationality : Vietnamese Previous Degree : B.Sc. (Chemistry) Hanoi University Scholarship Donor : Ecumenical Scholarship Program (ESP) Asian Institute of Technology Bangkok, Thailand August, 1996 ii ACKNOWLEDGMENT First of all I would like to express my profound gratitude and sincerest appreciation to my advisor, Dr. C. Visvanathan for his encouragement, unending support and valuable advice throughout the study period. My gratitude is extended to Mrs. Samorn Muttamara and Dr. Nguyen Thi Kim Oanh for their valuable advice and kindly serving as committee members. Appreciation is greatly extended to the Ecumenical Scholarship Program (ESP) for providing financial support for my study at AIT, and to the DANIDA for supporting research grant. Sincere thanks are due to Dr. Tran Van Nhan and the Center for Environmental Science and Technology, Hanoi University of Technology for their help and support during my field study in Vietnam. I would like to express my sincere thanks to Dr. Mark Radka of UNEP for providing necessary information and sharing his experience with me. My thanks is extended to all staff in the Technical Department of the Van Diem mill for their help in my field study in the mill. I would like to thank all faculty, staff and friends of EEP (SERD) at AIT for their help and cooperation. Finally, I wish to express my extreme gratefulness to my beloved parents and my brother for their unending love and encouragement. My sincere thanks is extended to my husband for his helpfulness, encouragement and moral support during my research period. I would like to dedicate this piece of work to my beloved parents. iii ABSTRACT Van Diem Paper Mill is a small integrated paper mill that uses bagasse and waste paper as raw material. The mill manufactures carton board, cover paper, pupil note-book cover. It was found that upsets and spills occurred frequently as a result of the old process. The production capacity was found to be 9 tons/day when the mill was running normally. Water balance, material balance and energy balance were drawn for the mill. The water consumption on an overall basis was found to be 376 m3 per ton of product. The suspended solid (SS) in the wastewater was 431.8 kg/ton of product. The fiber loss from the paper machines was considerable with the value of 20.8%. The total of SS and SS70 (parameter used to assess the fiber loss of a paper mill) discharged to the Red river was 369.7 kg/ton and 211.7 kg/ton respectively. The high concentration of alkaline vapour (0.187 mg/L) in the digestor plant was a severe source of air pollution in the mill. The cleaner production opportunities for the mill were studied. Stream segregation with black liquor collection could reduce pollution load. Good-housekeeping was especially recommended such as repairing all leakage, keeping taps closed when they are not in use and cleaning rolls in paper machines. TABLE OF CONTENTS CHAPTER TITLE PAGE Title Page i Acknowledgment ii Abstract iii Table of Contents iv List of Figures v List of Tables vi List of Illustration vii I. INTRODUCTION 1 1.1 General 1 1.2 Objective 2 1.3 Scope and Limitation of the Study 2 II. LITERATURE REVIEW 3 2.1 General Production Process of Pulp and Paper Industry 3 2.2 Source of Water Pollution and Its Characteristic 10 2.3 Environmental Problem from Pulping Processes 11 2.4 Raw Material for Pulping 12 2.5 Cleaner Production for Small Pulp and Paper Mills 15 2.6 An Overview of the Pulp and Paper Industry in Vietnam and Related Environmental Issues 16 2.7 Bench Marks in Pulp and Paper Industry 17 III. BACKGROUND INFORMATION OF THE RESEARCH SITE 3.1 General Information 19 3.2 Production Processing 19 3.3 Existing Water Supplied 22 3.4 Existing Wastewater System 22 3.5 Existing Fiber Recovery Unit 26 3.6 Working Environment and Environmental Issues of the Mill 26 3.7 Energy Consumption 26 IV. METHODOLOGY 4.1 Study Program 30 4.2 Data Collection 30 4.3 Inplant Monitoring 30 4.4 Material Balance and Energy Balance 30 4.5 Water Balance 30 4.5.1 Water Supplied Measurement 30 4.5.2 Wastewater Measurement 31 4.5.3 Sampling 32 4.5.4 Water and Wastewater Characterization 33 4.6 Fiber Recovery Unit Study 33 4.7 Physical Agents in Working Environment 4.7.1 Noise Measurement 33 4.7.2 Particulate Matter 36 V RESULTS AND DISCUSSIONS 5.1 Bench Mark of Pulp and Paper Mill 38 5.1.1 Raw Water Used in the Pulp and Paper Mill 38 5.1.2 Wastewater from Production Process 39 5.1.3 Energy Consumption of the Mill 40 5.2 Waste Auditing of Pulp and Paper Mill 40 5.2.1 Unit Operation of the Mill 40 5.2.2 Water Consumption 42 5.2.3 Accounting for Total Wastewater 44 5.2.4 Evaluating Material Balance 48 5.2.5 Summary 52 5.3 Energy Auditing of the Mill 53 5.3.1 Energy Consumption 53 5.3.2 Summary 54 5.4 Fiber Recovery Unit Study 54 5.4.1 Wastewater Quality and Fiber Recovery Efficiency 54 5.4.2 Determination of Settleable Solid of the Effluent 55 5.5 Noise and Air Pollution in the Work Environment 56 5.5.1 Noise 57 5.5.2 Particulate Matter 55 5.6 Identification for Cleaner Production Oppotunities 58 5.6.1 Causes of Waste Generation 58 5.6.2 Cleaner Production Oppotunities 59 5.7 Options of Cleaner Production Opportunities 60 IV CONCLUSIONS AND RECOMMENDATIONS 6.1 Water and Energy of the Mill 64 6.2 Noise and Air Pollution in the Mill 65 6.3 Recommendation on Cleaner Production Opportunities 65 REFERENCES APPENDICES LIST OF FIGURES FIGURE TITLE PAGE 2.1 Simplified Diagram of Pulp and Paper Process 4 2.2 Flowchart of Mechanical Pulping Process 5 2.3 Sulphite Pulping Process 7 2.4 Semichemical Pulping Process 9 2.5 Cleaner Production Techniques 15 3.1 Location of the Van Diem Paper Mill 20 3.2 Layout of the Van Diem Paper Mill 21 3.3 Simplified Diagram of Pulp and Paper Production of the Mill 23 3.4 Pulp Production Diagram of the Mill 24 3.5 Paper Production Diagram of the Mill 25 3.6 Water Supplied System of the Mill 26 3.7 Wastewater Drainage System of the Mill 27 3.8 Steam Distribution System of the Mill 29 4.1 General Methodology Outline 31 4.2 Flowrate Measurement Equipment 32 4.3 Wastewater Sampling Points and Wastewater Flow Measurement Points 33 4.4 Raw Water Sampling Points and Water Supplied Flow Measurement Points 34 4.5 Settleable Solid Measurement Using Imhoff Cone 37 4.6 Sound Level Meter Used for Noise Measurement 37 LIST OF TABLES TABLE TITLE PAGE 2.1 Typical Analytical results for Pulp and Paper Mill Waste 10 2.2 Chemical Composition and Fiber Dimension of Agricultural Residue-based and Wood Based Raw Material 13 2.3 Wash Filter Loading and Dewatering Properties of Various Sulphate and Soda Pulp 14 2.4 Bench Marks for Pulp and Paper Production 17 2.5 Wastewater Pollution Load in Agricultural Residue-based Mill 18 4.1 Analytical Parameters, Locations and Methods Used during the Study 35 ix ABBREVIATION BL : Black Liquor BOD : Biochemical Oxygen Demand COD : Chemical Oxygen Demand Cond. : Conductivity CP : Cleaner Production I : Investment Costs kg/ton : kg/ton of product L : Litre L/s : Litre per second Lpm : Litre per minute P : Pay Back Period PM : Paper Machine RM : Raw Material Preparation S : Saving Money SS : Suspended Solid SS70 : Suspended Solid (filter 70 µm) Temp. : Temperature TS : Total Solid CHAPTER 1 INTRODUCTION 1. General Paper is becoming an essential commodity of today’s society. The pulp and paper industry has been growing with demand of paper. The capita consumption has also been steadily increasing over the world. The pulp and paper industry is considered as one of the major potential sources of pollution in the environment. There are two segments, pulping and paper making in the manufacturing process. Pulping is the major source of environmental pollution. Black liquor from chemical pulping processes is the most significant and troublesome source of pollution. Effluent from these pulping processes contains chemicals which are known to cause damage to the flora and fauna . Also, bottom deposits of lignin cellulose material near the point of discharge undergoes slow decomposition that leads to depletion of dissolved oxygen in the receiving body. The raw materials for pulp production are those containing cellulose fibers. They are divided into two main types: wood and non-wood materials. Environmental problems on a global scale of deforestation is occurring. Therefore, using non-wood fiber material for paper production is encouraging. Although non-wood fibrous raw material based account for only about 5% of the raw material for pulp and paper manufacture today it is one of the major sources of fibrous raw material for many developing countries (GIERTZ, 1993). Agricultural residues are the most important raw materials of non- wood group that were used in agriculture countries. In developing countries, the small scale mills are more popular than large ones. Small scale mills usually cause high level of environmental pollution because of outdated technologies, poor operational and maintenance practices and others. On the other hand agricultural residues are especially suitable for small scale mills as their raw materials. However, using agricultural residues satisfies in terms of reducing the burden on forest wood, it has its adverse environmental impacts in term of pollutant discharge. Pulp and paper production is an important contributor to the economy of many nations. In Vietnam, the industry accounted for 1.8 per cent of the output value of the manufacturing sectors. Despite its increase in production capacity, it has not met the domestic consumption demand. The utilization of sugar cane bagasse as raw material for the pulp and paper industry needs some attention in sugar cane producing countries such as Vienam. It contributes to reducing deforestation as well as using by-product from the sugar industry. However, small paper mills using sugar cane bagasse as raw material have caused environmental pollution at high levels. -2- Therefore, cleaner production study in the small mill using sugar cane bagasse as raw material for pulp and paper production is useful in terms of economy as well as environmental protection aspect. An essential step in implementing cleaner production is waste audit as it gives a comprehensive look at production process to facilitate the understanding of material flows and to show pollution sources within the process. A waste audit points out the points specific area where pollution reduction may be achieved and helps to implement maximum resource optimization and improved process performance (UNEP/IEO and UNIDO,1991). This study investigated the current environmental status of a pulp and paper mill in small scale in Vietnam and recommended cleaner production practices for the mill. 2. Objectives The objectives of the study are: 1. To identify and evaluate sources and causes of waste generation of the pulping and paper making processes with a view to find out the extent of all environmental pollution problems, major focus on waste stream. 2. To determine the quantity and characteristic of wastewater discharges in pulp and paper mill which use non-wood material as raw material. 3. To identify possibilities to conserve water and to minimize pollution load. 4. To recommend cleaner production practices to the mill. 3. Scope and Limitation of the Study This study was limited only to a small scale pulp and paper industry using sugar cane bagasse as raw material. Initial investigation of environmental status of the mill included water, air and noise pollution but the major task focused on wastewater. The study on implementing cleaner production was concentrated on process effluent reduction and recovery as well as recycling rather than the process modification. CHAPTER II LITERATURE REVIEW 2.1 General Production Process of Pulp and Paper Industry The manufacture of paper can be divided into two phases: the pulping and the paper making. In the pulping phase the cellulose raw material must be processed to free fibers with suitable properties for paper product. The paper making is the continuous process consisting of forming slurried pulp in sheet form then pressing, drying, calendering. The simplified flow diagram of pulp and paper production process is shown in Figure 2.1. 2.1.1 Pulping The pulping process can be divided into three categories: chemical pulping, mechanical pulping, and semi-chemical pulping (combination of two above categories). Mechanical pulping Mechanical pulp is produced by grinding or shredding the wood or non-wood materials to free the fibers. In addition heat and pressure may be applied to assist the process. Mechanical pulping provides low grade pulps with high color and short fibers, but with a high yield converting 95% of the wood into pulp and produces minimal on-site air pollution and relatively water loads (ANONYMOUS 1981). The mechanical pulping process is presented in Figure 2.2. 1) Stone Groundwood Pulping The first grinders were built by Voith in 1852. In this method logs of wood are ground against a stone wheel to produce clumps of fiber. Stone groundwood does have some favourable characteristics : low energy costs and high fines content which is desirable for printing characteristics. 2) Refiner pulping The first attempt to use disc refiners to produce mechanical pulps was made in the 1950's. This demonstrated that it was possible to produce pulp which was stronger than stone groundwood (Mc CUBBIN, 1984). Thermo-mechanical pulping (TMP) process was developed. -4- This technique involves presteaming of chips for a short period, typically about three minutes, at a 110-130oC and 150-210kPa and then performing the first stage of refining under pressure (Mc CUBBIN, 1984). 3) Pressurized Groundwood Pressurized Groundwood (PGW) is a relatively new development. It is similar to the stone groundwood process but logs is ground under pressure. Generally speaking, the production of mechanical pulps has been limited to the use of soft woods preferably spruce, balsam and hemlock and , to a lesser extent, jack pine(due to a lower pulp quality). TMP has pulp yield of approximately 94% and the published data on BOD discharge varies from about 15 kg/t to 35 kg/t.(MCCUBBIN, 1984) Mechanical pulping provides a short pulp fiber due to the considerable fiber damage caused by grinding. Chemical pulping Chemical pulping is done by digesting to free fibers from the wood chips, non- wood materials such as bamboo, straw, grass, cotton, in chemical solutions that help to dissolve the lignin binding material. Pulp yield is normally in the range of 35 to 57% and about 95% of the lignin is removed in pulping (MCCUBBIN, 1983). Chemical pulps may be subdivided into Kraft (sulphate), sulphite, semi-chemical and soda. Soda pulping The soda pulping was the first chemical process applied in pulp manufacture. In the process, sodium hydroxide is used as cooking liquor with adding a mixture of soda ash (Na2CO3) and lime Ca(OH)2 to the digester. This process is most suitable for agricultural residues pulping (PALMER et al., 1983). Sulphite Pulping Process The sulphite pulping process is one of the major pulping methods. This process is most suitable for non-resinous softwood. In this method, the fibre-binding lignin is softened and dissolved to a considerable extent in a solution containing dissolved SO2, hydrogen sulphite ions with pH value between 1.5-12. Depending on the cooking degree, the yield varies from 45 to 65%, but normally the yield is about 50% for standard non- bleached pulps. If the pulp is bleached, another 4 to 5% of the original wood weight may be lost in the process. (ANONYMOUS, 1982). An advantage of the kraft pulping process is the possibility of recovering both process chemicals and the heat content of the dissolved lignin. One drawback is that the process results in pulps with a high kappa number which thus require bleaching for many applications. The sulphite pulping process is illustrated in Figure 2.3. 3/ Kraft Pulping Process -5- Kraft pulping, first used in 1879, is a modification of the caustic soda process in that sodium sulphite (Na2S) is added to the cooking liquor. The presence of caustic soda in the cooking liquor is suitable for use of practically all wood species. Sodium sulphate is on duty of buffering, that digestion can be implemented at a lower OH- ion concentration. Thus damage to the fibers is reduced and high strength pulps is produced (UNEP, 1977) 4/ Semi-chemical Pulping In this process the pulping of wood raw material pulp is obtained by a series of chemical and mechanical wood treatments. The main semi-chemical pulping process are: • Neutral sulphite, in which the active chemical is sodium sulphite, sufficient alkali ( usually sodium carbonate or sodium bicarbonate) is used to keep the digestion liquor alkaline. • Cold soda, in which chips are soaked for several hours in sodium hydroxide at atmospheric pressure without heating. The simplified flow sheet of semi-chemical pulping process is presented in Figure 2.4. 5/ Other processes According to PALMER (1983) recognizing the difficulties of using established processes on a small scale, a number of alternative processes are being developed which are claimed to be specially suitable for small-scale operation either because they are non-polluting (in at least one case it is claimed that digestion liquor can be used as fertilizer) or because the recovery process is relatively simple. Examples of these processes are: • Ammonia-based pulping. • Oxygen (air) and alkali processes. • Universal process (acid based). 2.1.2 Paper making In the paper making process pulp is converted into paper. Normally, the process consists of four main steps: stock preparation, sheet preparation, water removal and sheet finishing. Pulp in the stock is heated and mixed. Some different chemicals and fillers like alum, clay, and starch are added to the pulp stock for enhancement of certain paper properties. Next, the pulp is evenly distributed over a travelling belt of fine wire screening, and carried to rolls. A small portion of the water contained in the pulp passes through the screen, while the longer fiber are laid down on the wire , pressed through a series of rolls then air dried in a steam-heated dryer section. After drying, the sheet may be surface treated and then finished. A considerable portion of the fine fibers and some -6- fillers also pass through the screen wire with water . Because of its colour, this wastewater is called "white water". The main sources of waste from paper mills are beaters and paper machines. 2.2 Sources of Water Pollution and Its Characteristics The pulp and paper industry is one of the largest water- using industries, not only in terms of the volume specific water use, but also in terms of the volume of output. The sources of the wastewater in the pulp