dc.description.abstract | Thermal oxidation is one of the most effective processes for the treatment of VOC-containing gas stream. Especially, regenerative thermal oxidizer (RTO) has been developed to reduce energy consumption. For the operation of RTO, the VOC removal efficiency achieved with two-canister RTO is greatly reduced during valve switching. In this research, buffering module is applied to improve the VOC removal efficiency achieved with two-canister RTO. The concept is to fill the volume between the desorbing fan and the RTO with clean air prior to valve switching. Although leakage may still occur, high-concentration VOCs is not leaked. Because clean air is purged through the switching process, overall VOC removal efficiency achieved with the RTO system can be maintained. In this study, two facilities equipped with two-canister RTO were selected for investigation. The capacity of RTO#A was 166.3 CMM as designed, while the capacity of RTO#B was 87.2 CMM. Mass balance of the RTO system is performed to get the mass flow rates at the RTO system inlet, the zeolite concentrator outlet and the RTO outlet, respectively. The removal efficiency was calculated on the basis of the mass flow rate to restore the true removal efficiency of the system. Before the buffering module was installed, the overall removal efficiency of VOC achieved with RTO#A was 72.66%. After the installation of buffering module, the removal efficiency of VOCs achieved with the RTO#A system was increased to 91.59%. The mass flow rate of VOCs emitted from RTO#A was reduced to 0.3 kg/hr. The case of RTO#B was also investigated and it was a wrong design. The effectiveness of the buffering module is not as expected as the result of RTO#A. The VOCs removal efficiency achieved with RTO#B decreases during the actuation of the valve switching process, which is similar to the RTO#A before buffering module was installed. In addition, RTO#B also leads to too much air due to improper design and it, is equivalent to double of purge air in the three-canister RTO to perform the purge process. It aggravates the energy consumption problem. Regarding the manufacturing cost, the cost of the two-canister RTO is about NT$700,000, which is less expensive than the three-canister RTO. If the buffering module is added, the extra cost is about NT$450,000. The overall manufacturing cost is not as low as expected. Thus, three-canister RTO or rotary-type RTO is recommended for the new facility when considering RTO as the option for VOC removal to avoid additional cost and implementation time for subsequent improvement. | en_US |