Light Reflux Research Articles

Hollow Fibers Structured Packings in Olefin/Paraffin Distillation: Apparatus Scale-Up and Long-Term Stability

Following the conceptual demonstration of high separation efficiency and column capacity obtained in olefin/paraffin distillation using hollow fiber structured packings (HFSPs) in a bench scale (J. Membr. Sci.2006, 2007, and 2010), we scaled-up this process with a 10-fold increase in the internal flow rate and a 3-fold increase in the module length. We confirmed that the HFSPs technology gives high separation efficiency and column capacity in iso-/n-butane distillation for 18 months. We systematically investigated the effects of packing density, concentration of light component, reflux ratio, and module age on the separation efficiency and operating stability. Comprehensive characterizations using scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) were carried out to probe the changes in the morphological, thermal, and mechanical properties of polypropylene (PP) hollow fibers ove...

Experimental Study of a Dual Reflux Enriching Pressure Swing Adsorption Process for Concentrating Dilute Feed Streams

A dual reflux (DR) enriching pressure swing adsorption (PSA) process with two beds and an intermediate feed located at z/L = 0.5 was studied experimentally for concentrating a dilute feed of ethane in N2 using MeadWestvaco BAX-1500 activated carbon. A five-step cycle was used with feed, light reflux, and heavy reflux steps carried out simultaneously, and cocurrent depressurization and heavy product pressurization steps carried out simultaneously during different segments of the cycle. A parametric study showed that the light reflux flow rate, feed/heavy reflux step time, heavy product flow rate, and ethane feed mole fraction all had significant effects on the process performance in terms of purity and recovery. It also showed that it was relatively easy to concentrate ethane using a pressure ratio of only 7. The average of 19 runs with an ethane feed concentration of 1.38 vol % gave an ethane enrichment of 45.8 (63.2 vol %) and ethane recovery of 84%, while producing N2 at high purity (99.8 vol %) and rec...

Heavy reflux PSA cycles for CO2 recovery from flue gas: Part I. Performance evaluation

This study evaluated nine stripping PSA cycle configurations, all with a heavy reflux (HR) step, some with a light reflux (LR) step, and some with a recovery (REC) or feed plus recycle (F+R) step, for concentrating CO2 from stack and flue gas at high temperature (575 K) using a K-promoted HTlc. Under the process conditions studied, the addition of the LR step always resulted in a better process performance; and in all cases, the addition of a REC or F+R step surprisingly did not affect the process performance except at low feed throughputs, where either cycle step resulted in a similar diminished performance. The best cycle based on overall performance was a 5-bed 5-step stripping PSA cycle with LR and HR from countercurrent depressurization (CnD) (98.7% CO2 purity, 98.7% CO2 recovery and 5.8 L STP/hr/kg feed throughput). The next best cycle was a 5-bed 5-step stripping PSA cycle with LR and HR from LR purge (96.5% CO2 purity, 71.1% CO2 recovery and 57.6 L STP/hr/kg feed throughput). These improved performances were caused mainly by the use of a very small purge to feed ratio (γ=0.02) for the former cycle and a larger one (γ=0.50) for the latter cycle. The former cycle was good for producing CO2 at high purities and recoveries but at lower feed throughputs, and the latter cycle was useful for obtaining CO2 at high purities and feed throughputs but at lower recoveries. The best performance of a 4-bed 4-step stripping PSA cycle with HR from CnD was disappointing because of low CO2 recoveries (99.2% CO2 purity, 15.2% CO2 recovery and 72.0 L STP/hr/kg feed throughput). This last result revealed that the recoveries of this cycle would always be much lower than the corresponding cycles with a LR step, no matter the process conditions, and that the LR step was very important to the performance of these HR cycles for this application and process conditions studied.

Carbon dioxide capture from flue gas by pressure swing adsorption at high temperature using a K‐promoted HTlc: Effects of mass transfer on the process performance

AbstractUsing hundreds (640) of simulations obtained from a cyclic adsorption process simulator, two heavy reflux (HR) pressure swing adsorption (PSA) cycles were analyzed at the periodic state for the capture and concentration of CO2 from flue gas at high temperature (575 K), using a K‐promoted hydrotalcite like compound (HTlc). Since the values of the adsorption (ka) and desorption (kd) mass transfer coefficients of CO2 in the K‐promoted HTlc were uncertain, this study focused only on the effects of ka and kd on the process performance. Both, a 5‐bed 5‐step stripping PSA cycle with light reflux (LR) and HR from LR purge and a 4‐bed 4‐step stripping PSA cycle with HR from countercurrent depressurization were studied using a vacuum swing cycle with the high pressure fixed at 137.9 kPa and the feed set at 15 vol % CO2, 75 vol % N2, and 10 vol % H2O. For the 5‐bed process, increasing both ka (= 0.0058 s−1) and kd (= 0.0006 s−1) by a factor of five increased both the CO2 purity and CO2 recovery, achieving a CO2 purity of nearly 90% at a CO2 recovery of 72% and feed throughput (θ) of 57.6 L STP/h/kg. Increasing ka and kd by a factor of ten further increased both the CO2 purity and CO2 recovery, achieving for the first time a CO2 purity greater than 90% at a CO2 recovery of 85% and θ of 57.6 L STP/h/kg. Making kd = ka (= 0.0058 s−1) resulted in a CO2 purity of 89% with a CO2 recovery of 72% at a θ of 57.6 L STP/h/kg; and increasing that value by a factor of five led to a CO2 purity of 91% at a high CO2 recovery of 88% and θ of 57.6 L STP/h/kg. These results suggested that the performance was desorption limited. For the 4‐bed process, when ka and kd were both increased by a factor of five, the CO2 purity increased to 98% at a θ of 201.7 L STP/h/kg, but the CO2 recovery decreased to 5%. Overall, it was proven that mass transfer effects were important to the performance of this high temperature CO2 recovery process, with higher but acceptable values of ka and kd leading to CO2 purities of greater than 90%, a needed limit for process viability. © 2006 American Institute of Chemical Engineers Environ Prog, 2006

Stripping PSA Cycles for CO2 Recovery from Flue Gas at High Temperature Using a Hydrotalcite-Like Adsorbent

A cyclic adsorption process simulator was used to study novel high-temperature pressure swing adsorption (PSA) cycles. Based on the use of a K-promoted hydrotalcite-like (HTlc) adsorbent and six different (vacuum swing) stripping PSA cycles, these cycles were designed to process a typical stack gas effluent at 575 K containing 15 vol % CO2, 75 vol % N2, and 10 vol % H2O into CO2-depleted and CO2-enriched streams. More than a thousand (1260) simulations were conducted to the periodic state to study and interpret the effects of the light-product purge-to-feed ratio, the cycle step time, the high-to-low pressure ratio, the heavy-product recycle ratio, and the feed throughput (θ) on the process performance. The cycle configuration was changed from 4-bed 4-step, 4-bed 5-step, and 5-bed 5-step designs that utilized combinations of light-reflux (LR) and/or heavy-reflux (HR) steps, and cocurrent depressurization (CoD) and/or countercurrent depressurization (CnD) steps. The process performance was judged in terms of the CO2 purity in the heavy product (yCO2,HP), with the CO2 recovery (RCO2) and θ both being secondary process performance indicators. Any PSA process with a HR step outperformed any PSA process with only a LR step, regardless of whether a CoD step was added or not. The best performance was obtained from the 4-bed 4-step stripping PSA cycle with HR obtained from the CnD step, with yCO2,HP = 82.7 vol %, RCO2 = 17.4%, and θ = 14.4 L STP h-1 kg-1. The next best performance was obtained from the 5-bed 5-step stripping PSA cycle with LR and HR obtained from LR purge, with yCO2,HP = 75.5 vol %, RCO2 = 48.8%, and θ = 23.1 L STP h-1 kg-1. Overall, this study further substantiated the feasibility of a high-temperature stripping PSA cycle for CO2 concentration from flue gas using an HTlc adsorbent. It also disclosed the importance of the PSA cycle configuration to the process performance, by gaining an understanding of and appreciation for the use of HR, and it exposed the rigor involved in determining the best PSA cycle sequence for a given application.

Pigmentary glaucoma: a clinical review of anterior segment pigment dispersal syndrome.

Sixty-eight cases (44 males, 24 females) of anterior segment pigment dispersal syndrome are reviewed. Five patients had no rise in intraocular pressure, 38 had ocular hypertension and 25 had glaucoma as shown by optic disc cupping and field loss. All cases had heavy deposition of pigment in the drainage angle together with Krukenberg spindles and/or light reflux through the iris. Other evidence of anterior segment pigment dispersal was common. The condition was commonest in young adult males, but could present at any age and in women. Medical treatment was often successful initially, but continued to control pressure in only 17 of 42 patients. Laser trabeculoplasty helped some patients. Drainage operations of various types were successful in 19 of 23 cases. Iris angiography showed evidence of vascular hypoperfusion of the iris which probably precedes pigment dispersal and suggests that the ultimate aetiology may be a congenital deficiency of the mesodermal support tissues of the iris. Some degree of iris stromal atrophy is also common and may become marked. Pigment dispersal from the pigment epithelium of the iris occurs in susceptible individuals and may be associated with the insertion of the dilator muscle. The term anterior segment pigment dispersal seems appropriate as the condition is limited to the anterior segment.

Ocular involvement in scleroderma.

Thirty-eight patients with scleroderma (progressive systemic sclerosis) without renal failure were subjected to detailed clinical ophthalmic assessment. Abnormalities were frequent. However, many of these, including lens opacities, vitreous frosting, and arteriosclerotic changes, were considered to be age-related, and there were various incidental changes. Posterior subcapsular lens opacities in one patient were probably corticosteroid-induced. Changes related to scleroderma included eyelid abnormalities (stiffness or tightness in 11, telangiectasia in 8), deficient tear secretion (14 cases), and conjunctival abnormalities (injection 19 cases, vascular sludging 27 cases). Iris light reflux (6 cases) was possibly related to scleroderma. The changes related to scleroderma occurred in the 3 types classified according to the extent of skin involvement.