High-Efficiency PFC Abatement System Utilizing Plasma Decomposition and Ca(OH)$_{2}$ /CaO Immobilization
In order to minimize contributions to global warming, it is important to develop a perfluorocompound (PFC) abatement system that can remove PFCs effectively with low electric power. We have developed a new PFC abatement system consisting mainly of a 2-MHz ICP plasma source and two Ca(OH)2/CaO columns operated under a decompression pressure. Reactive fluorinated compounds including SiF4 are immobilized in the Ca(OH)2/CaO columns without a water scrubber. Stable compounds such as CF4 are excited by the 2-MHz ICP plasma. When the emissions from an Si oxidation film etching process chamber were treated by this abatement system, F2 equivalent removal efficiency was 99.6%, which was about one order of magnitude larger than that of a conventional abatement system. But the CO2 equivalent removal efficiency was calculated to be 91.4% because over 95% of CO2 equivalent emissions were caused by the plasma source power consumption of 2.4 kWh. It means that minimization of the plasma source power consumption, depending on PFC emissions, is a very effective method of minimizing contributions to global warming in a manner similar to improving the PFC removal efficiency.
CF/sub 4/ decomposition using inductively coupled plasma: effect of power frequency
The performance evaluation of CF/sub 4/ decomposition efficiency using 2- and 4-MHz power supplies was carried out as a function of the power, the pressure, the flow rate, and the quantity of O/sub 2/ addition. When the 2- and 4-MHz power supplies were used, almost complete CF/sub 4/ removal was achieved at 2.0 and 3.0 kW, respectively, when the CF/sub 4/ flow rate was 0.20 normal liters per minute. The optimum O/sub 2//CF/sub 4/ ratio should be in the range of 1.0/spl sim/1.25 in order to decompose CF/sub 4/ efficiently. The CF/sub 4/ decomposition efficiency using the 2-MHz power supply was significantly higher than that of the 4-MHz power supply under the same power, pressure, and flow rate. Significant amounts of byproducts such as COF/sub 2/ and CO were identified by the Fourier transform infrared spectrophotometer analysis in addition to CO/sub 2/.
Single-stage plasma-chemical process for particulates, NO/sub x/, and SO/sub x/ simultaneous removal
In a previous study, we investigated the simultaneous removal of NO/sub x/ and SO/sub x/ using a plasma-chemical hybrid process and showed nearly 100% of NO/sub x/ and SO/sub x/ removal. In this study, we investigated simultaneous removal of NO/sub x/, SO/sub x/, and particulates using a single-stage wet-type plasma reactor. This reactor consists of a discharge wire and pyrex cylinder, wrapped by the copper mesh where Na/sub 2/SO/sub 3/ and NaOH solutions flow along the inner wall of the cylinder from the top to the bottom of the reactor. Particulates are charged by pulse corona and collected on the inner wall, and then removed by solutions flow. This method is effective for extremely low. and high-resistivity particles to cause reentrainment or back corona. The plasma was used to oxidize NO to NO/sub 2/, Na/sub 2/SO/sub 3/ solution to reduce NO/sub 2/ to N/sub 2/ and Na/sub 2/SO/sub 4/, and NaOH solution to neutralize nitric and sulfuric acids in the solutions. Without Na/sub 2/SO/sub 3/ and NaOH solutions, 95% of NO removal and no SO/sub 2/ conversion were achieved at 2.5 W. With water, 97% of NO and 64% of NO/sub x/ removal were achieved at 2.6 W, and more than 95% of SO/sub 2/ removal was achieved regardless of the discharge power. With Na/sub 2/SO/sub 3/ and NaOH solutions, 98% of NO and 75% of NO/sub x/ removal were achieved at 2.9 W, and more than 93% of SO/sub 2/ removal was achieved regardless of the discharge power. For the purpose of enhancement of surface reaction on NO/sub 2/ reduction with Na/sub 2/SO/sub 3/, Raschig rings were placed beneath the plasma section with the effective lengths of 5, 10, and 15 cm. As a result, no significant NO/sub x/ removal was obtained in comparison with no Raschig rings. Regarding the removal efficiency of diesel soots using the plasma-chemical hybrid reactor, more than 90% of particulate removal efficiency was obtained.