| Summary: | 碩士 === 國立中山大學 === 環境工程研究所 === 102 === In the petrochemical process, due to process design, or actual handling safety requirement, even preventive safety, the gases generated from the process are discharged directly as waste gases to the flare for incineration. The combustion efficiency of flare is declared as high as 98%, but the emitted waste gas contains a lot of VOCs, though they are treated by incineration, some VOCs may not be destroyed completely and are emitted to the atmosphere. At present, the energy cost rises successively, hence, reducing the emission of the aforesaid air pollutants could not only attain the goal for energy saving and carbon reduction, but also reduces the costs (air pollution fee, fuel cost). Flare gas recovery is the most frequently used method. The gas recovery equipments in the process are used, or gas compressors are mounted at the pipe end to prevent the waste gases from entering the flare, so as to effectively reduce the emission of air pollutants from the flare.
This study investigated the process of a petrochemical factory by collecting the field data of flare gas recovery and utilization systems of flare gas recovery system, waste gas burning system and furnace, including chemical composition component of the recovered flare gases, flow rate and flue gas analysis. The influence of flare gas recovery on the gas burning system is calculated and discussed, including the influence of air pollutant emission, combustion efficiency, and greenhouse gas emission (e.g. CO2).
This study discussed the flare gas recovery and reuse of flare gases, including direct recovery as products, or as fuels for various facilities, even for electric power plants. In Taiwan, no matter from the perspective of technology or feasibility, applying compressor to recover flare gases directly as fuel is feasible. The recovery ratio of two compressors operated in parallel can be increased from <40% to 75~85% in comparison to one single compressor. The recovered flare gas can be used as gas fuel. When the hydrogen content of the flare gas declined, the combustion efficiency of gas-fired boiler decreased. In other words, increasing the hydrogen content tended to increase the combustion efficiency of flare gases to some extent.
This study further discussed the cost-benefit of various recovery techniques. If the reciprocating compressor was used to recover flare gas as fuel for boilers, the payback period is 2.38 years. If the natural gas for gas generator is replaced by the recovered flare gas, the payback period is 2.38 years, too. In terms of gas-to-liquid (GTL technology), the payback period is estimated to be 3.12 years.
Moreover, flare gas recovery would reduce the consumption of boiler fuel, as well as the emission of greenhouse gases (GHGs) indirectly. Approximately 111,455 MT CO2 emission can be reduced annually with the reduction efficiency up to 83.3%.
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