| 摘要: | 變壓吸附法為一分離氣體混合物之連續性循環操作程序，利用氣體混合物中各成分對吸附劑之吸附能力的不同而產生的吸附選擇性達成氣體分離的效果，並利用高壓吸附、低壓脫附以得到高濃度的產物。由於氣體高壓吸附期間會釋放熱量，將增加吸附床溫度而不利於吸附進行，另一方面，氣體低壓脫附時為吸熱過程，將降低吸附床溫度而不利於脫附進行。因此本研究設計具有熱交換的不同結構型吸附塔，目標為將進行吸附步驟的床中所放出的熱量經由管壁傳至正在進行脫附步驟需熱的床，達到更佳的吸附及脫附效果。
本研究以zeolite 5A分離空氣製造氧氣，將空氣組成簡化為21%的氧氣、1%氬氣與78%的氮氣後，以extended Langmuir isotherm model描述其等溫平衡吸附曲線，再以線性趨動力質傳阻力模型描述其氣固間吸附質傳阻力。結果顯示具有熱交換的半圓柱型吸附塔和雙套管型吸附塔比起沒有熱交換的傳統獨立雙圓柱型吸附塔增加了熱補償效益，此效益有助於提升Skarstrom cycle分離空氣製造氧氣的氧氣濃度。
接著增加具有熱交換的吸附塔之塔數，結果顯示具有熱交換的吸附塔其塔數增加後，氧氣的純度會上升，且分割圓柱型吸附塔對於氮氧分離的效果較套管型吸附塔好。最後選擇六分之一圓柱型吸附塔作變因探討尋求計算數據中最佳的操作條件。最佳的操作條件為進料壓力為4.35 atm，塔長31.5 cm，進料加壓時間為48 s，高壓產氣時間為29 s。最佳的結果為塔頂產物氧氣濃度94.27%，回收率30.45%。
;Pressure swing adsorption (PSA) is a cyclic process to separate gas mixtures based on the difference of adsorption capacity of each component on adsorbent. This technology consists of gas adsorption at high pressure and desorption at low pressure to produce high-purity product. The heat released during gas adsorption will increase the bed temperature, which is unfavorable to adsorption. On the other hand, gas desorption is an endothermic process, which will decrease the bed temperature, so it is unfavorable to desorption. In this study, the traditional cylindrical adsorbers are replaced by heat-exchange divided cylindrical and concentric-tube adsorbers. To achieve better adsorption and desorption effects, the adsorption heat released from one bed during adsorption process can be transferred through the wall to the neighboring desorption bed which needs heat to desorb the adsorbing gases.
This study utilizes zeolite 5A to separate oxygen from air, and the air composition is simplified to 21% oxygen, 1% argon, and 78% nitrogen. The extended Langmuir isotherm model is used to describe adsorption isotherms of gas components. Linear driving force model is used to describe the mass transfer resistance between gas and solid phase. The results show that heat-exchange semicylindrical and concentric-tube adsorbers can have better heat compensation during adsorption and desorption, which increases the oxygen purity in Skarstrom cycle.
Furthermore, we study the effect of increasing the number of beds with heat-exchange adsorbers. The results show that when the number of beds with heat-exchange adsorbers increases, the purity of oxygen increases, and the air separation effect of divided cylindrical adsorbers is better than that of concentric-tube adsorbers. Finally, we chose one-sixth cylindrical adsorber to discuss operating variables, and explored the best operating conditions among all the simulation results. The best operating conditions are feed pressure 4.35 atm, bed length 31.5 cm, pressurization time 48 s, and production time 29 s. The simulation results of the best conditions are 94.27% purity and 30.45% recovery of oxygen at top product. |
