การศึกษาใช้ฟองอากาศระดับไมครอนสำหรับล้างทำความสะอาดผงถ่านหิน

Abstract

At this time, Thailand has been using natural gas as its main fuel in electricity generation at the present time. A number of these reserved natural gases are likely to be dramatically decreased in the future. However, Thailand also has abundance of another fuel resource, which the lignite coals that are considered lower quality but cheaper compared to other fuel resources. Even though the coals is not fully accepted and bad reputation for its harmful impact on environment, it is being developed and used with Clean Coal Technology in order to lower the pollution from the coal combustion. The objective of this research is to apply microbubble for coal cleaning. In this study, the microbubble was produced by three different bubble generators: porous stones, ejector nozzle and ejector nozzle combine with pressure tank. The result shows that the size of bubbles produced by porous stones are appeared larger compares to the bubbles produced by the ejector nozzle are smallest. The average diameter of the bubbles from the porous stones and the ejector nozzle is about 385 μm and 85 μm, respectively. In addition, the bubbles from using the ejector nozzle combine with pressure tank are the smallest. The water becomes milky due to the presence of a lot of fine microbubbles. It was found that for case of pressure at 6 bar in compressed tank, the average diameter of the bubbles was 38-40 μm. In addition, the flow characteristics within the flotation column was studied, which the glass plate was installed at the central for dividing the flow channel. From the experiment, it was found that the height of the 50 cm glass plate allows the fluid to flow across the column longer than the 35 cm glass plate. Because the fluid can move in the first flow channel as the entrance is longer before recirculating back to the other side of the flow channel. For the study of cleaning and separating coal powder, the lignite coal samples were crushed to smaller than 250 μm. The 1 kg of coal powder mixed with 2 litre of water was added with diesel oil as collector for 8 kg/tons of coal and pine oil was added as frother for 0.15 kg/tons of coal. After that, the coal slurry was fed into the flotation column containing water of 22.5 liters. The water flow rate and air flow rate were kept constant at 20 litre/min and 0.7 litre/min, respectively. Moreover, the result of cleaning and separating coal powder was also investigates by using 3 bubble generators in order to carry the coal to the water surface or coals concentrate. For the coal cleaning, it is found that the bubbles from the ejector nozzle combined with pressure tank can carry largest amount of coal power to the water surface. The ejector nozzle and porous stones can separate lesser coal. In addition, microbubbles can be caught with the coal powder smaller than 150 μm, up to 93.1 percent of the total coal volume. While the proximate analysis of components in separated coal, it was found that the ash content and volatile matter content were decreased about 20.5% and 14.4%, respectively. On the other hand, the fixed carbon was increasing about 26.0%. In case of increasing pressure in the pressure tank from 3 bar to 6 bar, it was found that the coals concentrate was significantly increased. In addition, the ash content and volatile matter content were decreased about 45.5% and 21.5%, respectively. On the other hand, the fixed carbon was increasing about 38.8%. However, increasing the flotation time for cleaning and separating coal powder, the results show that the coals concentrate had decreased. While the ash content, sulfur content and volatile matter content were also decreased about 20.3%, 13.9% and 11.5%, respectively. On the other hand, the fixed carbon was increasing about 33.1% and the gross calorific value in coal was increases to 9.3%.