Analisi tecnico-economica del processo di upgrading del biogas mediante Pressure Swing Adsorption

La Pressure Swing Adsorption (PSA) è una tecnologia diffusamente applicata l'upgrading del biogas a biometano, soprattutto per impianti di relativamente piccola potenzialità. In questo studio viene presentato un modello di simulazione dinamica che descrive il funzionamento di unità multibed di PSA, a partire dalla conoscenza dell'equilibrio e della cinetica di adsorbimento dei due componenti da separare (anidride carbonica e metano) sul materiale adsorbente utilizzzato, e consente di valutarne parametri sintetici di performance quali la purezza del biometano prodotto, il recupero di metano, la produttività, i consumi energetici. Il modello è stato utilizzato per analizzare diversi cicli e condizioni operative: in particolare, a partire da un ciclo base, con le classiche fasi di pressurizzazione, alimentazione/adsorbimento ad alta pressione (3-5 atm), blow-down e spurgo sotto vuoto (0.1 atm), sono stati studiati cicli che includono step di equalizzazione della pressione, in modo da ridurre i consumi energetici e migliorare il recupero del metano; per ogni sequenza sono riportati i risultati di diversi test run, modificando le variabili di progetto in modo da ottenere una specifica di purezza >97% (come richiesto attualmente per il gas naturale immesso nella rete gas italiana) con un recupero elevato (>85%) e consumi energetici bassi. Lo studio effettuato indica che, a partire da biogas al 50% di metano, è possibile ottenere la specifica di purezza richiesta con recuperi intorno al 90% e consumi di energia del 2.5-3% del contenuto energetico del biometano ottenuto; il recupero aumenta e il consumo energetico all'1.5-2% se il biogas ha un contenuto di metano del 65%. Sulla base dei dimensionamenti effettuati si è stimato un costo per un impianto di upgrading di circa 530 Nm3/h di biogas (potenzialità corrispondente all'ottenimento di 1 MWel ) intorno ai 1200-1600 k e, tenendo conto dell'ammortamento del capitale, degli oneri finanziari e dei costi di esercizio, un costo del biometano ottenuto di 0.25 /Nm3, per un biogas al 50% di metano, o inferiore a 0.2 /Nm3 se si alimenta l'impianto con un biogas al 65% di CH4. Questo costo deve essere aggiunto al costo di produzione del biogas, al costo del pretrattamento del biogas per la rimozione di umidità e inquinanti (in particolare H2S) e tutti i costi relativi all'immissione in rete. E' inoltre necessario considerare il problema della destinazione dell'olio-gas, che ha un contenuto di metano dall'8 al 18% e dal quale dovrebbe essere recuperata energia termica. Un confronto con la tecnologia a membrana, sviluppato facendo in particolare riferimento ai risultati ottenuti da ENEA Trisaia, indica che la PSA consente di ottenere recuperi maggiori con consumi energetici più bassi; nel caso della separazione con membrana i consumi energetici vanno dal 4.4 % (recupero del 75%) al 5.8% se si vuole ottenere un recupero del 94.5% (in questo caso, però il biometano è reso alla pressione di 31 atm)

Utility of ultrasound assessment of diaphragmatic function before and after pulmonary rehabilitation in COPD patients

Claudia Crimi,1 Enrico Heffler,2 Teresa Augelletti,2 Raffaele Campisi,1 Alberto Noto,3 Carlo Vancheri,4 Nunzio Crimi2 1Respiratory Medicine Unit, AOU “Policlinico-Vittorio Emanuele”, Catania, Italy; 2Respiratory Medicine Unit, Department of Clinical and Experimental Medicine, AOU “Policlinico-Vittorio Emanuele”, University of Catania, Catania, Italy; 3Anesthesia and Intensive Care Unit, AOU Policinico “G. Martino”, Messina, Italy; 4Regional Referral Centre for Rare Lung Diseases, A.O.U. “Policlinico-Vittorio Emanuele”, Department of Clinical and Experimental Medicine, University of Catania, Catania, Italy Background: Pulmonary rehabilitation (PR) may improve respiratory symptoms and skeletal muscle strength in patients with COPD. We aimed to evaluate changes in ultrasound (US) measurements of diaphragmatic mobility and thickness after PR in COPD patients and to test its correlation with PR outcomes.Methods: Twenty-five COPD patients were enrolled and underwent a diaphragm US assessment before and after a 12-week PR program.Results: We found a correlation between the intraindividual percentage of change in the diaphragmatic length of zone of apposition at functional residual capacity (ΔLzapp%) and the change in 6-minute walking distance (6MWD) after PR (rho=0.49, P=0.02). ΔLzapp% was significantly higher in patients with improved 6MWD and COPD Assessment Test (CAT) score (mean rank=12.03±2.57 vs 6.88±4.37; P=0.02). A ΔLzapp% of ≥10% was able to discriminate among patients with improved 6MWD, with a sensitivity of 83% and a specificity of 74%. The area under the receiver operating characteristic curve for ΔLzapp% was 0.83. A cutoff value of ≥9% of ΔLzapp% had a positive predictive value in discriminating a reduction in ≥2 points of CAT score after PR, with a sensitivity and a specificity of 80% and 62%, respectively.Conclusion: Diaphragm US assessment represents a useful prognostic marker of PR outcomes in COPD patients. Keywords: diaphragm ultrasound, COPD, pulmonary rehabilitatio

Obstructive sleep apnoea syndrome and the metabolic syndrome in an internal medicine setting

Background: Obstructive sleep apnoea syndrome (OSAS) is widely accepted as a cardiovascular risk factor. Lately it has been considered in turn as both a component and one of the causes of the metabolic syndrome (MS). Methods: We studied 281 heavy snorers of both sexes consecutively attending a metabolic clinic. Aim was to evaluate the association of OSAS and MS in a large series of patients within an internal medicine setting. Patients underwent a clinical and biochemical work up and performed unattended polysomnography. Results: Of 226 non-diabetic snorers, 48 had primary snoring; 54 mild, 51 moderate, and 73 severe OSAS. A positive association was found between OSAS severity, central obesity indices and the mean metabolic score (p = 0.016). Prevalence of hypertension increased with OSA severity (p = 0.010). Polysomnographic indices were correlated with the metabolic score, insulin levels and central obesity indices. At regression analysis, male sex (t = 3.92; p = 0.000) and waist circumference (t = 3.93; p = 0.000) were independently associated with AHI (apnoea/hypopnoea index), while ODI (oxygen desaturation index) and waist circumference were the independent predictors (t = 2.16; p = 0.033 and t = 3.74; p = 0.000 respectively) of the metabolic score. Prevalence of OSA was 83% in 55 patients with diabetes and 34% had severe OSA. Almost all diabetics with OSA had MS. The metabolic score was higher in diabetic OSA as compared to non-diabetic OSAS (p = 0.000). Conclusions: Our findings show a high prevalence of OSAS among patients referred to a metabolic outpatient clinic because of suspected metabolic disorders and heavy snoring and suggest a strong bidirectional association between OSAS and MS. (C) 2010 European Federation of Internal Medicine. Published by Elsevier B.V. All rights reserved

Biogas upgrading through CO2 removal by chemical absorption in an amine organic solution. Physical and technical assessment, simulation and experimental validation

An experimental and modelling study of CO2 removal from a simulated biogas feed by chemical absorption in an organic solution of 2-amine-2-methyl-1-propanol in an ethylene glycol and n-propanol solvent is presented. Absorption was carried out under different temperature, feed flow rate, and feed recirculation conditions. Regeneration was carried at different temperatures. Cyclability tests showed that the absorption capacity remained stable starting from the fourth cycle. In the conditions analyzed, higher temperatures and liquid recirculation favor absorption. With all other conditions constant, the CO2 absorption efficiency increased from 72% to 87% when the temperature increased from 23 to 45°C. At 33°C, liquid recirculation enhanced the absorption efficiency from to 93%–97%. A model was developed and validated against experimental results. Absorption and desorption rates are proportional to the carbon dioxide and AMP concentrations and to the alkyl carbonate concentration, respectively. The two rate constants were fitted from the experimental data: their values at 30°C are 0.033 s−1 (kmol/m3)−1 and 1.5 × 10−6 s−1, respectively. The model indicates that the beneficial effect of temperature and liquid recirculation is due to the increased mass transfer coefficient of CO2 from the gas to the liquid solution, which increased from 4 × 10−3 s−1 at 20°C to 1.3 × 10−2 s−1 at 70°C and by a factor of 8.8 as a consequence of feed recirculation. An increase in the biogas flow rate reduced the absorption efficiency by decreasing the contact time. Higher temperatures also increased the rate of CO2 desorption