EVALUATION OF COMBINED DEINKING PROCESS AND NOVEL UTILIZATION OF DEINKING SLUDGE

Abstract

There is an increasing need for recycling. However, for recycling of paper, conventional method of chemical deinking is used but it needs further improvements to make the quality of recycled fibres reach up to that of virgin fibres, as far as possible. Hence, the present work is focused on evaluation of combined deinking process. Moreover, increase in recycling increases the production of waste called deinking sludge. This waste creates disposal problem. Hence, this work also focuses on the utilization of deinking sludge for useful energy recovery as well as for the production of building materials like brick. This research work is divided into four chapters: Chapter 1 gives general introduction about the issues and challenges being faced by Indian recycled paper industry. It also discusses and highlights the objectives and scope of the present work. Chapter 2 focuses on the studies on deinking processes using combined deinking and chemical deinking technologies. Combined deinking refers to the application of UV irradiation and ultrasound treatment on chemically deinked pulp. Photocopier waste paper was used as the raw material for this study. The optimization of duration of application of UV irradiation and ultrasound treatment was carried out to study their effects on the effectiveness of deinking processes. This was accomplished by evaluating various properties obtained after the application of selected treatments. The comparison of properties was carried out among all the three deinking processes. It appears that the combined deinking technology produced better results as compared to chemical deinking for most of the optical as well as strength properties. Hence, combined deinking technology can further improve the deinkability potential of chemical deinking. Chapter 3 focuses on the thermal conversion of deinking sludge and its kinetics. This work is further divided into two parts. Two separate deinking sludge namely deinking sludge (A) and deinking sludge (B) were used as raw materials for section one and section two respectively. First part studies the effect of different heating rates on the pyrolysis and combustion of deinking sludge (A). In this section four heating rates namely 10, 20, 30 and 40 °C/min were applied under nitrogen and air atmospheres. Second part studies the thermal processing of deinking sludge (B), coal (C), rice husk (RH) and their blends under nitrogen and air atmosphere. In this section, 10 °C/min heating rate was applied throughout the experiment. It ii was found that blending of deinking sludge with coal improves the ignition characteristics and shows higher reactivity compared to only coal. Hence, utilization of deinking sludge with coal can improve performance of the pyrolysis and combustion processes of coal. In addition, it was found that combustion improved the degradation process of deinking sludge, coal and rice husk. Blending of deinking sludge up to 20 wt% with coal displays almost similar combustion profile as that of coal. Thus deinking sludge can be used with coal in the existing combustion system. Moreover, it was observed that the deinking sludge required higher burnout temperature as compared to rice husk. The reactivity decreased with increment in amount of deinking sludge in the blend with rice husk. It was found that the rice husk replacement by deinking sludge up to 20 wt% showed almost similar pyrolysis profile as that of rice husk. The results obtained in such experiments may be used for effective design of thermal co-processing systems. Chapter 4 investigates the utilization of deinking sludge in fired clay bricks. Initially the characterization of raw materials namely clay and deinking sludge was carried out using characterization techniques like XRF, XRD, TGA and SEM. Then different mixing proportions were prepared with deinking sludge with clay and fired at three different temperatures namely 900 °C, 950 °C and 1000 °C. Different properties of fired clay bricks were obtained using various codal standards for all temperatures. From the investigation, it was observed that the 15% deinking sludge addition in fired clay brick is optimum. Moreover, it is observed that the firing temperature of 950 °C is optimum. The values of compressive strength and water absorption were found too well under the limits mentioned in the standard IS 1077:1992. This lies under the class 10 that is suitable for brick masonry work. Also, it was noted that the thermal conductivity decreased with increase in the amount of deinking sludge addition. Reduction in thermal conductivity is suitable for energy saving purposes. Hence, deinking sludge can be effectively used in fired clay bricks, which can not only save energy but can also address the problem of disposal of deinking sludge.