變壓吸附法的學習控制於放射線氪及氙氣的純化設計

核電廠的放射線廢氣處理主要技術為木炭床吸附分離，此分離技術單純是以巨型的管柱延遲放射線廢氣Kr-85 (氪)及Xe-13(氙)為目的，而其中微量的Kr-85半衰期長達10.76 年，長期以來一直被忽略，導致大氣中Kr-85 在全球排放總量已經超過背景值數千倍。因此以生活環境及人體安全為前提，使用傳統拖延方式是無法解決目前問題，本研究利用純化分離技術手段，期望能封存最高純度的放射性Kr 氣及Xe 氣，同時縮減管柱大小使吸附劑能不斷的連續進行純化及再生利用。本研究採用變壓吸附法(pressure swing adsorption，PSA)作為放射線廢氣中Kr氣的純化，PSA 是一個仿連續操作的吸附及再生系統，利用高壓吸附及低壓脫附再生的循環操作原理，比較起傳統方式更能有效的減少廢氣處理系統空間及成本。但是PSA 為一個多變數的複雜分離系統，如何有效地找出最佳分離操作條件是重要的，利用離線式基因演算法(Genetic Algorithms，GA)計算最佳化的搜尋方法。一般核電廠會從排放廢氣中所含的放射性廢氣(Kr、Xe)之濃度判斷廠內是否有異常現象發生，若在運轉過程中濃度異常上升使放射線廢氣排放超過法規限定值，嚴重時必須停止反應爐運轉勢必造成莫大損失。因此在設計PSA 時除了解決放射性廢氣異常濃度外，製程運行中常見的吸附劑老化導致吸附力逐漸衰退現象，修正控制設計是必需的，利用疊代學習控制法(iterative learning control，ILC)修正操作條件，使系統能在異常濃度下仍達到欲分離的純度期望值。放射線廢氣中的Xe-133，通常延遲數天無害後當廢氣處理，但它在空氣中僅含0.9x10^-5%是一種高價值的稀有(noble)氣體，可應用於汽車燈、奈米材料及半導體高分子聚合物等應用，亦可將其純化後再利用，因此本研究將三種類型的PSA，Modify-PSA、Vacuum-PSA及Idle-PSA，進行分析與比較測試Kr 及Xe 氣純化的效果，最後也利用多變數ILC修正異常狀況找回最佳值，使放射線廢氣分離技術更加完善。

關鍵字

吸附；氣體純化；氪氣；基因演算法；核廢氣處理；變壓吸附

並列摘要

The main technology in the treatment of radiation off-gas is gas solid adsorption(GSA) separation system which uses huge columns to delay the radioactive isotopes of Krypton and Xenon. However, tracing Krypton-85 with half-life of 10.76 years has long been ignored, causing global atmospheric Krypton-85 content to exceed the background value several thousand times. On the premise of natural environments and human health, traditional delay technology cannot solve the current problem. In this work, purifying separation techniques are used to achieve high-purity radioactive Krypton and Xenon, reduce column volume, achieve continuous purification and recycle the adsorbent. In this work, pressure swing adsorption (PSA) is used to purify radioactive off-gas of Krypton. PSA is a continuous operation of the adsorption and regeneration system. Based on the operating principle of high-pressure adsorption and low-pressure desorption regeneration cycle, it is more compact and economical than traditional methods. PSA is a multivariable complex separation system. In this research, a genetic algorithm is used to effectively identify the optimum separation operation conditions. In general, the concentration of the radioactive off-gas in the emission can be used to detect any fault in the operation. If the concentration exceeds the regulations limit, in severe cases, the nuclear reactor will have to be shut down and cause a great loss in profits. Therefore, it is essential for PSA to handle the abnormal concentration and the decrease in adsorption capacity caused by the decay of the adsorbent control design. Iterative learning control (ILC) is used to adjust the operation condition so that the desired purity can still be attained under abnormal concentrations. Another radioactive off-gas, Xenon-133, which is harmless after a few days, is often emitted as waste. However, it is a high-value tracing noble gas with applications in car lights, nano-materials and semiconductor polymers, so it should be purified for usage. In this study, a continuous purification of the Krypton and Xenon gases using a multi-bed PSA is proposed. Comparisons between the multi-bed PSA and three typical PSA modes, including Modified-PSA, Vacuum-PSA and Idle-PSA, are made in order to analyze and verify the separation performance. Like the single bed PSA, ILC control design is applied to the multi-bed PSA to make the system achieve desired purities even under abnormal concentration.

並列關鍵字

Adsorption ； Gas purification ； Krypton ； Genetic algorithm ； Nuclear reprocessing ； Pressure swing adsorption

參考文獻

1. L. B. Batta, to Union Carbide Corporation, U.S. Patent 3,636,679 (1972).

3. A. I. Bolozdynya, P. P. Brusov, T. Shutt, C. E. Dahl and J. Kwong, "A Chromatographic System for Removal of Radioactive 85Kr from Xenon," Nuclear Instruments and Methods in Physics Research Section A, Vol.579, No.1, p.50-53 (2007).

7. F. A. Da Silva and A. E. Rodrigues, "Propylene/Propane Separation by Vacuum Swing Adsorption Using 13X Zeolite," AIChE Journal, Vol.47, No.2, p.341-357 (2001).

8. J. A. Delgado and A. Rodrigues, "Analysis of the Boundary Conditions for the Simulation of the Pressure Equalization Step in PSA Cycles," Industrial and Engineering Chemistry, Vol.63, No.18, p.4452-4463 (2008).

9. J. A. Delgado, M. A. Uguina, J. L. Sotelo, V. I. Águeda and P. Góme, "Numerical Simulation of a Three-bed PSA Cycle for the Methane/Nitrogen Separation with Silicalite, " Separation and Purification Technology, Vol.77, No.1, p.7-17 (2011).

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變壓吸附法的學習控制於放射線氪及氙氣的純化設計

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