DEVELOPMENT OF SIMULTANEOUS PROCESS TECHNOLOGY FOR PRODUCTION OF HIGH PURITY AMORPHOUS BIO-SILICA FROM RICE HUSK AND UTILIZATION OF ITS COMBUSTION ENERGY

• Main Author: Steven, Soen
• Format: Dissertations
• Language: Indonesia
• Subjects: Teknologi kimia industri
• Online Access: https://digilib.itb.ac.id/gdl/view/70069
• Institution: Institut Teknologi Bandung

Rice husk has great potential to produce chemicals and energy. The high content of ash and silica in the ash (bio-silica) makes it a source of silica in large quantities from renewable and inexpensive raw materials. The aim of this study is to produce high purity and amorphous bio-silica from rice husk and the utilization of its combustion energy. Interestingly, there are still few studies that focus on those two products. Ash production is carried out by rice husk combustion and the ash is then extracted to obtain bio-silica. The remaining combustion energy is utilized for small-scale electricity generation. The limitation of this operating condition is the amorphous silica phase so that the combustion should not be above 700oC. One of the prevention is using excess air. The study starts with a study of bio-silica production from rice husk ash and ends with a study on rice husk combustion. The stages of the study was producing amorphous bio-silica through chemical extraction of rice husk ash, three-dimensional flow simulation studies and cold test experiments in an acrylic suspension furnace, simulation of rice husk combustion with a realistic decomposition approach, experiments on rice husk combustion in a suspension furnace, and energy utilization simulation. The bio-silica production study aimed to examine the variations of leaching sequences on bio-silica characteristic, solvent to feed (S/F) ratio, extraction time, and refining. The leaching variations were AE (leach-extract-dry), EA (extract-leach-dry), EAD (extract-dryleach), and without leaching as a control. Leaching used HCl and extraction was held with NaOH. The acid leaching is important to eliminate mineral impurities while refining process is for removing carbon content. The results indicated all of the amorphous biosilica was amorphous. Variations AE, EA, EAD, and control gave amorphous bio-silica with purity of 95.70%, 87.69%, 62.40%, and 56.93% and surface area of 277.49 m2/g, 55 .49 m2/g, 11.40 m2/g, and 5.72 m2/g, respectively. The precipitation using HCl and H2SO4 did not affect the bio-silica yield and purity significantly. The most optimal condition was extraction under the S/F ratio of 6 for 1 hour, resulted in 85.4% of yield with a purity of 95.5%. The second stage of study investigates the rice husk and air flow pattern in an acrylic suspension furnace under simulation. The rice husk particle sphericity enhancement and size reduction is important for it could reduce the escaped particle and maximizes the fluidparticle contact in the furnace. The feeding pipe orientation should also be sunk to reduce the particle backflow out from the feeding location for the consequence of vacuum pressure generation. the remaining escaped particle is handled by cyclone installation. The tangential pipe declination of 75o provides the highest turbulence turbulent intensity, swirl amount, particle path length, and particle residence time. In addition, four-secondary air pipe with the declination of 60o lower the escaped particle as well as increase the air particle intensity by creating a recirculation zone in the bottom area of the combustor and elevate the particle residence time. In addition, the shifting of feed properties from rice husk to rice husk ash, as well as shifting of temperature from 25–700oC intensify the escaped particle. Meanwhile, from the cold test experiment, air swirl flow is indicated by the oil paper movement upward and downward forming a curve and circular directions. On the other hand, the rice husk swirl flow structure is indicated by the exhibition of sinusoidal peaks and valleys in the burner. The prediction of the escaped particle behavior has a good compliment with all of the cold test experiment results. The third stage investigates the devolatilization of rice husk using a realistic decomposition approach to form gas (64.78%), liquid/tar (7.28%), solid/char (27.94%). Under oxidation with 100% of excess air, as much as 2.6 MJ/kg of specific combustion energy is produced. The thermodynamics simulation expressed that NOX emission amount from rice husk combustion is negligible and there is still a probability for CO and H2 to be produced at above 500oC. It is found that combustion equipped with larger excess air reduce the combustion efficiency but could maintain the temperature at 700oC. Supplying excess air of about 180–200% is finally advantageous to keep the combustion temperature, to avoid silica crystalline formation which harms human health, as well as to suppress NOX and CO emissions. The study concluded that a realistic decomposition approach could predict the rice husk combustion performance with reasonable and logical results. The rice husk combustion study in a suspension furnace was initially conduced by ignition test in a fixed bed furnace. The ignition temperature of rice husk was above (428????8)oC. Combustion was then performed using 500 gram of rice husk char as fuel and the rice husk feeding was held when it reaches the ignition point. The ratio of total air to biomass was set at 8.5. The variation of the feed flow rate used was 9.27, 20.23, 25,20, 31.36, and 42.51 kg/h. The feeding was stopped until it reached 2500 gram for the first 4 variations and reached 500 gram for the last variation. From this experiment, the flame in the combustion lasted in 15–30 minutes and the it was continued with glowing combustion which was the key to the successful conversion to ash. The highest temperature of combustion was recorded at 552–560oC. The yield of produced ash was 18.94–23.68% with silica content in the ash of 88.29–89.15%. Ash was in the amorphous phase with the unburned carbon content of 5.11–23.27%. This supports the need for a refining process. This study finally offers the concept of production process integration of amorphous bio-silica from rice husk and the utilization of its combustion energy