Influence of product flow rate on O2 volume fraction in PSA oxygen generation process
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摘要: 為了提高小型兩床變壓吸附（PSA）制氧機在變產品氣流量下的氧氣體積分數，建立了改進的Skarstrom兩床循環PSA制氧實驗裝置，研究了產品氣流量對其氧氣體積分數的影響。研究結果表明，在低產品氣流量運行條件下，通過提高清洗氣總氧量與原料氣總氧量之比（P/F）以及降低最高吸附壓力與最低解吸壓力之比（θ）可消除氧氣返混的不利影響；在高產品氣流量運行條件下，通過提高P/F和θ可以提高實驗裝置中分子篩的工作能力，進而提高產品氣中的氧氣體積分數。在此基礎上，對低和高產品氣流量運行條件下的P/F和θ進行了調節，分別將產品氣流量為3.55 L·min?1和19.88 L·min?1時的氧氣體積分數從92.4%增加至了95.7%和從74.0%增加至了74.9%。本文的研究結果可為變產品氣流量下PSA制氧工藝參數優化提供參考。Abstract: In recent decades, the small-scale pressure swing adsorption (PSA) oxygen generator has been widely used in the fields of home medical and hospital oxygen supply, anoxic environments, and plateau environments due to its cost effectiveness, operational flexibility, and adequate O2 volume fraction. The flexible optimization of PSA oxygen generation in response to changes in product demand is an important factor in its practical performance. To study the influence of a variable product flow rate on O2 volume fraction in the small-scale PSA oxygen generator, experimental equipment was set up, which consisted of a modified Skarstrom-cycle two-bed PSA system. The research results show that variations in the parameters at the lower product flow rate (≤10.37 L·min?1) may have a negative effect on oxygen countercurrent mixing, which can impair oxygen generation, and at higher product flow rates (≥13.57 L·min?1) may cause the negative effect of nitrogen breakthrough, which decreases the working capacity of the adsorbents in the bed. The O2 volume fraction at the lower product flow rate was improved by increasing the ratio of total oxygen in the purge gas to the total oxygen in the feed gas (P/F) and by decreasing the ratio of the highest adsorption pressure to the lowest desorption pressure (θ) during a cycle to suppress oxygen countercurrent mixing. The O2 volume fraction at the higher product flow rate was improved by increasing the P/F and θ values to improve the working capacity of the adsorbents in the bed. Accordingly, adjustments are made in the P/F and θ values at the lower and higher product flow rates to achieve optimal oxygen generation performances, enhancing the O2 volume fraction from 92.4% and 74.0% to 95.7% and 74.9% at the respective product flow rates of 3.55 L·min?1 and 19.88 L·min?1. This work is meaningful for the optimization of the parameters of the PSA oxygen production process at variable product flow rates.
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圖 1 實驗裝置原理圖
Figure 1. Schematic of pressure swing adsorption (PSA) experimental setup
1—Filter; 2—Air compressor; 3—Heat exchanger; 4—Buffer tank; 5—Needle valves (K1−K4); 6—Relief valve; 7—Mass flowmeters (F1, F2, F3); 8—Solenoid valves (E1−E8); 9—Adsorption beds (B1, B2); 10—Pressure transducers (P1, P2); 11—O2 concentration detection ports (C1, C2, C3); 12—Check valve; 13—O2 storage tank; 14—Pressure maintaining valve; 15—PLC；16—Computer
圖 2 改進的Skarstrom兩床循環PSA工藝流程圖
Figure 2. Schematic of the modified Skarstrom pressure swing adsorption cycle
圖 3 實驗A和B中的氧氣體積分數和回收率隨產品氣流量的變化
Figure 3. Variations of O2 volume fraction and recovery rate with product flow rate in experiments A and B
圖 4 實驗A與B在產品氣流量為3.55 L·min?1時床層頂部氧氣體積分數和床層壓力隨循環時間的周期性變化
Figure 4. Cyclic variations of O2 volume fraction and pressure at the top of the bed in experiments A and B at a product flow rate of 3.55 L·min?1
圖 5 產品氣流量分別為3.55 L·min?1和10.37 L·min?1時，實驗B床層頂部氧氣體積分數和床層壓力隨循環時間的周期性變化
Figure 5. Variations of O2 volume fraction and pressure at the top of the bed at product flow rates of 3.55 L·min?1 and 10.37 L·min?1, respectively, in experiment B
圖 6 產品氣流量分別為13.57 L·min?1和19.88 L·min?1時，實驗B床層頂部氧氣體積分數和床層壓力隨循環時間的周期性變化
Figure 6. Variations of O2 volume fraction and pressure at the top of the bed at product flow rates of 13.57 L·min?1 and 19.88 L·min?1, respectively, in experiment B
圖 7 產品氣流量為3.55 L·min?1時實驗B和C床層頂部氧氣體積分數和壓力的變化
Figure 7. Variations of O2 volume fraction and pressure at the top of the bed in experiments B and C at a product flow rate of 3.55 L·min?1
圖 8 產品氣流量為19.88 L·min?1時實驗B和C床層頂部氧氣體積分數和壓力的變化
Figure 8. Variations of O2 volume fraction and pressure at the top of the bed in experiments B and C at a product flow rate of 19.88 L·min?1
圖 9 實驗B和實驗C在變產品氣流量下氧氣體積分數和回收率的比較
Figure 9. Comparison of O2 volume fraction and recovery at different product flow rates in experiments B and C
表 1 床層及有關管道尺寸
Table 1. Adsorption bed and related pipe sizes
Items Size/mm Diameter of adsorption bed 112.00 Column length of adsorption bed 620.00 Diameters of main pipe 19.05 Diameters of pressure equalization and purge pipe 12.70 
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表 2 吸附劑參數
Table 2. Adsorbent quantities and properties
Items Size Mass of oxygen molecular sieve 2.70±0.01 kg（one bed） Mass of activated alumina 0.76±0.01 kg（one bed） Average diameter of oxygen molecular sieve ～0.50 mm Average diameter of activated alumina ～4.00 mm Bulk density of oxygen molecular sieve 670.00 kg·m?3 Bulk density of activated alumina 700.00 kg·m?3
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表 3 PSA工藝步驟
Table 3. PSA cycle design at each step
Items Duration/s B1 B2 Items Duration/s B1 B2 Step 1 0.5 PPE&FP DPE Step 5 0.5 DPE PPE&FP Step 2 5 FP BD Step 6 5 BD FP Step 3 7 AD DP Step 7 7 DP AD Step 4 5 AD&PG PG Step 8 5 PG AD&PG
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表 4 P/F和θ隨產品氣流量增加的變化范圍
Table 4. Ranges of variations of P/F and θ with product flow rate
Experiment P/F θ A 1.33–0.74 3.29–3.10 B 0.65–0.49 3.55–3.33
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表 5 實驗B和C工藝參數的對比
Table 5. Comparison of process parameters in experiments B and C
Product flow rates conditions Product flow rate/ (L·min?1) P/F θ Experiment B Experiment C Experiment B Experiment C Lower product flow rates 3.55 0.65 1.34 3.55 3.24 7.18 0.66 1.14 3.52 3.26 10.37 0.65 0.68 3.47 3.42 Higher product flow rates 13.57 0.64 0.65 3.44 3.42 16.73 0.57 0.58 3.40 3.39 19.88 0.49 0.51 3.33 3.36
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