The performance of pressure swing adsorption (PSA), membrane separation, and gas absorption systems for H2 recovery from refinery off‐gas stream was studied by simulation‐based data. The PSA process was simulated using adsorbents of silica gel and activated carbon for removing heavy and light hydrocarbons. The mole fraction profiles of all components and the relationship between hydrogen purity and recovery as a function of feed pressure were examined. The solution‐diffusion model was applied for modeling and simulation of a one‐stage membrane process. The gas absorption process with a tower tray was simulated at sub‐zero temperature and the correlation between hydrogen purity and recovery as a function of tower pressure and temperature was evaluated at different solvent flow rates. 相似文献
Hydrogen was recovered and purified from coal gasification-produced syngas using two kinds of hybrid processes: a pressure swing adsorption (PSA)-membrane system (a PSA unit followed by a membrane separation unit) and a membrane-PSA system (a membrane separation unit followed by a PSA unit). The PSA operational parameters were adjusted to control the product purity and the membrane operational parameters were adjusted to control the hydrogen recovery so that both a pure hydrogen product (>99.9%) and a high recovery (>90%) were obtained simultaneously. The hybrid hydrogen purification processes were simulated using HYSYS and the processes were evaluated in terms of hydrogen product purity and hydrogen recovery. For comparison, a PSA process and a membrane separation process were also used individually for hydrogen purification. Neither process alone produced high purity hydrogen with a high recovery. The PSA-membrane hybrid process produced hydrogen that was 99.98% pure with a recovery of 91.71%, whereas the membrane-PSA hybrid process produced hydrogen that was 99.99% pure with a recovery of 91.71%. The PSA-membrane hybrid process achieved higher total H2 recoveries than the membrane-PSA hybrid process under the same H2 recovery of membrane separation unit. Meanwhile, the membrane-PSA hybrid process achieved a higher total H2 recovery (97.06%) than PSA-membrane hybrid process (94.35%) at the same H2 concentration of PSA feed gas (62.57%).
The production of high purity hydrogen (99.99+%) at reduced cost is an important and sought target. This work is focused on the separation of hydrogen from a five component mixture (H2/CO2/CH4/CO/N2) by pressure swing adsorption. A complete mathematical model that describes the dynamic behaviour of a PSA unit is presented. This model is applied in the study of the behaviour of both single column and four columns PSA processes with layered activated carbon/zeolite beds and with an eight steps cycle. In the single column simulation, a 99.9994% purity hydrogen stream is attained at the end of the feed step for a process hydrogen recovery of 51.84% and a productivity of . The multicolumn simulation predicts a hydrogen recovery and purity, respectively, of 52.11% and 99.9958%. The influence of feed flow rate, purge to feed ratio and lengths of both adsorbent layers on the system performance is assessed. It is shown that the introduction of the zeolite layer improves both the purity and recovery of the process. Reduced models are formulated based on the sequential identification of controlling resistances in the complete model. The predictions of the reduced models are evaluated by comparing their results with those obtained from the complete model. It is shown that the model that merely takes into account the micropore resistance (described by the LDF model) and assumes thermal equilibrium only between the gas and solid phases satisfactorily predicts the behaviour of the pressure swing adsorption unit. 相似文献
Cycle sequence has an important effect on the performance of pressure swing adsorption (PSA) processes. Pressure equalization steps influence significantly the purity and recovery of product, and therefore, may be properly designed to improve the performance of PSA processes. Open literature lacks of a systematic study on the effect of cycle sequence design on the performance of a specific PSA process as a controlling parameter. In this work, the results of recent studies on different cycle schedule design strategies have been used as a basis for comparing various cycle schedules (proposed by the authors of this work) on the performance of a six-bed PSA process for hydrogen purification. Three different cycle sequences have been designed, the pressure equalization and idle steps consisting the main controlling parameters. Simulation results showed that designs with more pressure equalization steps result in higher product recovery and those with less pressure equalization steps result in higher product purity. The proper performance of a PSA process is a tradeoff between product recovery and product purity. In this view, a target function has been developed that enables us to lump the latter performance parameters into one function for comparing the performance of the different cycles employed. 相似文献
Methane steam reforming is the main hydrogen production method in the industry. The product of methane steam reforming contains H_2, CH_4, CO and CO_2 and is then purified by pressure swing adsorption(PSA) technology. In this study, a layered two-bed PSA process was designed theoretically to purify H_2 from methane steam reforming off gas. The effects of adsorption pressure, adsorption time and purgeto-feed ratio(P/F ratio) on process performance were investigated to design a PSA process with more than99.95% purity and 80% recovery. Since the feed composition of the PSA process changes with the upstream process, the effect of the feed composition on the process performance was discussed as well.The result showed that the increase of CH_4 concentration, which was the weakest adsorbate, would have a negative impact on product purity. 相似文献
An efficient design for pressure swing adsorption (PSA) operations is introduced for CO2 capture in the pre-combustion process to improve H2 recovery and CO2 purity at a low energy consumption. The proposed PSA sequence increases the H2 recovery by introducing a purge step which uses a recycle of CO2-rich stream and a pressure equalizing step. The H2 recovery from the syngas can be increased over 98% by providing a sufficient purge flow of 48.8% of the initial syngas feeding rate. The bed size (375m3/(kmol CO2/s)) and the energy consumption for the compression of recycled CO2-rich gas (6 kW/(mol CO2/s)) are much smaller than those of other PSA processes that have a CO2 compression system to increase the product purity and recovery. 相似文献
Abstract Pressure swing adsorption processes have been traditionally used to produce one high purity gas stream from a gas mixture. One of the most common uses of this technology is in the production of ultrahigh purity hydrogen from various gas streams such as steam methane reformer (SMR) off-gas. However, many of these gas streams contain a second gas in sufficiently high concentrations, e.g., carbon dioxide in SMR off-gas, that the recovery of this secondary gas stream along with the primary product is extremely desirable. A new pressure swing adsorption (PSA) process, GEMINI-8, has been developed at Air Products and Chemicals, Inc., to achieve this goal. Process cycle steps for the GEMINI-8 PSA process are illustrated by SMR off-gas fractionation for the production of hydrogen and carbon dioxide. Capital and power savings of this process as well as other advantages compared with the previous technology are discussed. 相似文献
Huge amounts of global warming gas emissions have prompted interest in the recovery of H2 from off-gases in the iron and steel industries. Pressure swing adsorption (PSA) processes with layered beds packed with zeolite 5A and activated carbon were applied for H2 recovery from coal gas with relatively low H2 concentrations (H2/CO2/CH4/CO/N2; 38/50/1/1/10 vol.%). Breakthrough curves in the layered bed showed behavior results between the zeolite 5A bed and the activated carbon bed. The bed with the higher zeolite ratio produced H2 of higher purity in the PSA operation, but recovery loss became more significant with its increasing ratio. The variation of purity and recovery by operating variables were more significant in the two-bed PSA process than they were in the four-bed PSA process. The purity in the two-bed PSA varied asymptotically according to P/F ratio in the range of 0.1–0.3, while purity variation in the four-bed PSA process was almost linear. The zeolite layer in the two-bed PSA process worked as a separator of N2, while that in the four-bed PSA process worked as a purifier of N2. The four-bed PSA process could produce H2 with a purity of 96–99.5% and a recovery of 71–85% with N2 as the major impurity. The dynamics of the breakthrough and H2 PSA processes were studied using a non-isothermal dynamic model. 相似文献
An experimental study was performed for the recovery of CO2 from flue gas of the electric power plant by pressure swing adsorption process. Activated carbon was used as an adsorbent.
The equilibrium adsorption isotherms of pure component and breakthrough curves of their mixture (CO2 : N2 : O2=17 : 79 : 4 vol%) were measured. Pressure equalization step and product purge step were added to basic 4-step PSA for the
recovery of strong adsorbates. Through investigation of the effects of each step and total feed rate, highly concentrated
CO2 could be obtained by increasing the adsorption time, product purge time, and evacuation time simultaneously with full pressure-equalization.
Based on the basic results, the 3-bed, 8-step PSA cycle with the pressure equalization and product purge step was organized.
Maximum product purity of CO2 was 99.8% and recovery was 34%. 相似文献
A pressure swing adsorption (PSA) process for separating CO from a COCO2N2 mixture is proposed. The adsorbent used in this process is active carbon supported copper, which has been developed by this laboratory. By cycling the pressure of a bed of this adsorbent between ambient pressure and 20–30 Torr at room temperature, high purity CO can be obtained from the COCO2N2 gas mixture with a high recovery. The CO product purity depends crucially on the step of CO cocurrent purge after adsorption in the cycle and the regeneration of sorbent. 相似文献
Abstract High-purity hydrogen is commercially produced by pressure swing adsorption from hydrogen-rich mixtures. In this work, a vacuum pressure swing adsorption cycle is used to produce high purity hydrogen from a hydrogen-lean binary mixture (20/80 H2/CO) using zeolite 5A as the sorbent. The effects of different process variables on separation performance have been studied. The purity of hydrogen product increases at low throughput, high feed pressure, high end pressure of cocurrent depressurization, low end pressure of countercurrent evacuation, and short cycle time. Also, it was found that for a H2-lean mixture, the separation is improved at higher ambient temperature. In addition, a new “vacuum purge” step was found to improve the separation and is therefore a promising step for commercial application. 相似文献