| Summary: | 碩士 === 國立交通大學 === 環境工程系所 === 95 === In the high-tech industry, small local scrubbers with low flow rate are usually installed at the exhaust end of the process equipments to treat residual gases. They are important tail-pipe equipments for removing process exhaust gases. Local scrubbers have several types such as electric heating-wet scrubbing, combustion-wet scrubbing, packed tower scrubbing and dry adsorption. Among them, small packed towers are the primary equipments for controlling acidic and basic waste gases. However, factors such as residence time of gas flow, the inlet concentration of gas pollutants, quality of re-circulating water and its pH value, and gas-liquid ratio, all of them will affect the absorption efficiency and they are worth to be investigated. Also it is necessary to improve the gas absorption efficiency of the scrubbing tower.
Previous researches indicate that the abatement efficiency of HF, HCl, and NH3 by the packed tower scrubber is not very well. This research intends to design and test a highly efficient small-scale honeycomb type packed tower to improve the removal efficiency of acidic and basic gases. In the front of the scrubber, the water droplets will be sprayed to absorb and remove the waste gas. The removal efficiency will be further increased by the larger surface area offered by a honeycomb type packed tower (surface is wetted by water spray) installed at the rear end of the scrubber. The exhaust gas flow rate is produced by fax that is designed to 209~2,694 L/min, and the residence time at the front-end spray tower and the rear-end honeycomb packed tower are 0.5~10 sec and 0.5~2.5 sec, respectively. The parameters to be investigated in my research are included the residence time of gas flow, inlet concentration of gas pollutants, and gas-liquid ratio. In addition, the relationship between the overall removal efficiency and the specific surface area of the honeycomb packed tower, the wetting flow rate, and the pressure drop of the gas flow will be studied.
The experimental result showed that, for the HCl, when the inlet concentration is more than 400 ppb, the removal efficiency is 90%. As the inlet concentration increase, the removal efficiency will become into a stable value, 98~99% by using honeycomb packed tower scrubber. For honeycomb section at low flowrate(670 lpm), the total removal efficiency can be raised 5% to 85% for HCl in 500 ppb of the inlet concentration; then, 50 ppb of the inlet concentration, the total removal efficiency also can be raised 15~20% to 95%. In others words, the lower inlet concentrations, the higher improvement of the total removal efficiency, as the similar result as air flowrate is 1855 lpm; for NH3, when the inlet concentration is more 2000 ppb, the total removal efficiency will become 80%, and if it below 2000 ppb, it will be decrease rapidly by the inlet concentration. Even the NH3 pass through the honeycomb packed tower, the efficiency doesn’t rise anymore. This situation is obvious under very low concentration.
For honeycomb packed tower treat HCl, the inlet concentration is 400 ppb, the total removal efficiency is 90%. There is no different between honeycomb packed tower and honeycomb packed tower scrubber. Undoubtedly, the honeycomb packed tower also has high removal efficiency for low concentration of the HCl. However, the total removal efficiency for NH3 is not very well. When the NH3 inlet concentration is more than 2000 ppb, the total removal efficiency is closed to 60~65%.
We compare gas to liquid ratio between 19.3 and 53.4. We found that there is no different between them for removal efficiency curve, because both of them of the residence time are too long to distinguish. Their residual time are both more than 2.0 second.
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