Quanli Zhang

The massive emission of low-concentration coal mine methane (CMM) has resulted in the ineffective utilization of a large amount of energy methane and caused environmental pollution. The gas mixture used in the study consisted of methane (CH₄) 12% and nitrogen (N₂) 88%. The adsorbent was coconut activated carbon. This paper uses the adsorption method to conduct enrichment research on 12% low-concentration CMM. Firstly, the variation in methane gas concentration under different desorption methods was studied by numerical simulation, and the desorption methods suitable for increasing methane concentration were analyzed. A three-bed VPSA CMM separation experimental device was built, and three enrichment processes of feed gas pressurization, exhaust gas pressurization, and vacuum exhaust (VE) were studied. The results show that using the three-bed vacuum pressure swing adsorption (VPSA) process can effectively enrich low-concentration CMM. Under the adsorption pressure of 110 kPa and the desorption pressure of 10 kPa, 12% of CMM can be enriched to more than 25%, with a recovery rate higher than 80%. The exhaust process can significantly increase the product gas concentration. The product gas concentration increased by 18.2%, with the product rising from 22.5% to 26.6% when the extraction step increased from 0 s to 8 s. This research may provide reliable fundamental data for industrial-scale low-concentration CMM enrichment.

In oxygen production on plateaus, pressure swing adsorption (PSA) oxygen production is currently the most commonly used oxygen production method. In plateau regions, low pressure leads to a decrease in adsorbent nitrogen–oxygen separation performance, which affects the performance of PSA oxygen production, so it is particularly important to enhance adsorbent nitrogen–oxygen separation performance. In this paper, Li-LSX (lithium low-silicon aluminum X zeolite molecular sieve) adsorbents were modified using the liquid phase ion exchange method, and five kinds of modified adsorbents were obtained, namely AgLi-LSX, CaLi-LSX, ZnLi-LSX, CuLi-LSX, and FeLi-LSX, respectively. The influences of different metal ions and modification time lengths on the adsorbent nitrogen adsorption and nitrogen–oxygen separation coefficients were analyzed. Through theoretical calculations, the nitrogen and oxygen adsorption and separation performances of the modified adsorbents at different altitudes and low adsorption pressures were investigated. It is shown that the nitrogen adsorption capacity of the AgLi-LSX-1 adsorbent obtained from the modification experiment reaches 27.92 mL/g, which is 3.24 mL/g higher than that of Li-LSX; the nitrogen–oxygen separation coefficients of S1 and S2 are 19.24 and 7.54 higher, respectively; and the nitrogen–oxygen separation coefficients of S4 are 20.85 and 7.54 higher than those of Li-LSX, respectively. With the increase in altitude from 50 m to 5000 m, the nitrogen–oxygen separation coefficient of the AgLi-LSX-1 adsorbent increased rapidly from 20.85 to 57, and its nitrogen–oxygen separation coefficient S4 exceeded that of the Li-LSX adsorbent to reach 47.61 at an altitude of 4000 m. Therefore, the modified adsorbent AgLi-LSX-1 in this paper can enhance the performance of the PSA oxygen process for oxygen production in plateau applications.

In recent years, the number of people driving from plain areas to the western plateau of China has been increasing, and their safety is threatened by acute high-altitude reactions caused by hypoxia. Vehicle-mounted pressure swing adsorption oxygen supply technology can help solve this problem. For the optimization of vehicle pressure swing adsorption oxygen production, the influence of different pressure equalization methods on oxygen production efficiency was studied. The best oxygen production performance was achieved when the initial upper pressure equalization method and the simultaneous pressure equalization method were used. Using a 160 W air compressor, the product gas flow rate could reach 2.5 L/min with an oxygen concentration of 93.48%. The impact of adsorption time, equalization time, flow rate, and throttle inner diameter on oxygen concentration and recovery rate was analyzed using the response surface method. The order of the four factors affecting oxygen concentration is as follows: flow rate > adsorption time > equalization time > throttle inner diameter. After optimization, the product gas flow rate was 2.6 L/min, the oxygen concentration was 92.11%, and the oxygen recovery rate was 44.51%.