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.
PFC recycling system by continuous gas chromatography
We propose a new system to reduce emissions of Perfluorocompounds (PFCs) from semiconductor industries by continuous gas chromatography technology. For example, the recycling technology that was suggested before, such as cryogenic distillation, has some problems in its repurification step. It needs a huge distillation tower and much power for refrigeration. The continuous gas chromatography technology is a compact alternative to the conventional technology. This system is composed of the series of separation columns, vacuum pumps, and sequentially controlled valves. The mixture of PFCs is separated by the difference of the affinity for the filling material in the column. Only pure PFCs separated perfectly are outputs and the others are injected to the next column. By recycling the mixture of PFCs, which was not separated by single column, the continuous gas chromatography outputs the pure PFCs continuously. Moreover, it can experimentally separate CF/sub 4/-NF/sub 3/, which cannot be separated by a cryogenic distillation. Based on the accumulation and consideration of experimental data, we realized the continuous efficient separation of CF/sub 4//C/sub 2/F/sub 6/ with the large-scale pilot plant of the continuous gas chromatography. In this method, a high recovery rate of more than 99% was obtained and residual C/sub 2/F/sub 6/ in recovered CF/sub 4/ and residual CF/sub 4/ in recovered C/sub 2/F/sub 6/ were less than 0.01%. This recycling system is compact and it can operate with low-energy consumption.
Towards Ideal NO Control Technology Using a Plasma-Chemical Hybrid Process
The plasma-chemical hybrid process developed was extremely effective and economical in comparison with the conventional selective catalytic reduction (SCR) system and other technologies for NO removal from flue gas emissions. A series of experiments was performed to quantify all the reaction by-prod- ucts such as N O, CO, HNO , HNO , and NO and to evaluate NO removal efficiency. The optimum plasma reactor and its operating characteristics were investigated with regard to reaction by-products and NO removal efficiency using the ordinary ferroelectric packed-bed plasma reactor and the barrier-type packed-bed plasma reactor. The oxidation from NO to NO without decreasing NO concentration (i.e., minimum reaction by-products) and with least power consumption is the key for the optimum reactor operating condition. The produced NO was totally converted to N and Na SO with Na SO scrubbing. The barrier-type packed-bed plasma reactor having 1.5-mm-diameter electrode and 3-mm-diameter BaTiO pellets showed the superior NO oxidation without producing the by-products over the conven- tional packed-bed reactor. The barrier-type packed-bed plasma reactor followed by the chemical reactor showed extremely low operating costs (less than 1/6 of the SCR process) and achieved nearly 100% NO removal with less than 6 ppm of N O and 5 ppm of CO.