Energy analysis of different municipal sewage sludge-derived biogas upgrading techniques

Biomass-derived energy sources are rising their importance since both public opinion and legislation are currently calling for a sustainable development. Biogas is an energy source which can come from municipal sewage sludge digestion thus coupling the advantages of being a renewable energy source and of allowing a smart waste reutilization. In order to fully exploit the biogas potential as vehicle fuel or natural gas substitute, biogas itself must be treated in order to obtain biomethane. Biogas upgrading, i.e., the treatment for CO2 removal, can be performed by several techniques, each one characterised by a different energy demand. Since no clear guidelines are given in literature for choosing among different biogas upgrading processes, this work presents a quantitative analysis, from an energy view point, of water scrubbing, MEA (monoethanolamine) scrubbing, and MDEA (methyldiethanolamine) scrubbing when applied to obtain biomethane from municipal sewage sludge-derived biogas. Heat and electrical power consumptions of each of the above mentioned processes have been obtained by means of process simulation with commercial packages (such as Aspen Plus®). The aim of the work is the energetic comparison among these different techniques. Such a comparison can help in assessing the impact of the biogas purification step on the energy balance of the whole biomethane production process

Refrigeration cycles in low-temperature distillation processes for the purification of natural gas

The increasing energy demand has made low-quality natural gas reserves worthy of consideration for exploitation. As a consequence, industries have developed new process solutions in order to exploit these gas reservoirs in a profitable way. Most of these solutions are natural gas purification processes by distillation at low-temperature, involving or not solid CO2 formation. Due to the low-temperatures reached in this type of processes, the choice of the appropriate refrigeration cycle becomes of paramount importance for limiting their energy consumptions and, thus, their operating costs. The aim of this work is to compare the performances of different types of refrigeration cycles using the coefficient of performance (COP) as discriminating factor. Several compounds (such as nitrogen, light hydrocarbons and ethylene) and their mixtures have been considered as working fluids and both non-cascade and cascade systems have been taken into account. Simulations by means of Aspen Hysys® V7.3 have led to conclude that the propane-ethylene cascade refrigeration cycle allows to attain the best performances

Gas holdup and flow regime transition in spider-sparger bubble column: Effect of liquid phase properties

This paper discusses the effects of the liquid velocity and the liquid phase properties on the gas holdup and the flow regime transition in a large-diameter and large-scale counter-current two-phase bubble column. In particular, we compared and analysed the experimental data obtained in our previous experimental studies. The bubble column is 5.3 m in height, has an inner diameter of 0.24 m, it was operated with gas superficial velocities in the range of 0.004-0.20 m/s and, in the counter-current mode, the liquid was recirculated up to a superficial velocity of -0.09 m/s. Air was used as the dispersed phase and various fluids (tap water, aqueous solutions of sodium chloride, ethanol and monoethylene glycol) were employed as liquid phases. The experimental dataset consist in gas holdup measurements and was used to investigate the global fluid dynamics and the flow regime transition between the homogeneous flow regime and the transition flow regime. We found that the liquid velocity and the liquid phase properties significantly affect the gas holdup and the flow regime transition. In this respect, a possible relationship (based on the lift force) between the flow regime transition and the gas holdup was proposed. © Published under licence by IOP Publishing Ltd

The dual effect of viscosity on bubble column hydrodynamics

Some authors, in the last decades, have observed the dual effect of viscosity on gas holdup and flow regime transition in small-diameter and small-scale bubble columns. This work concerns the experimental investigation of the dual effect of viscosity on gas holdup and flow regime transition as well as bubble size distributions in a large-diameter and large-scale bubble column. The bubble column is 5.3 m in height, has an inner diameter of 0.24 m, and can be operated with gas superficial velocities in the range of 0.004–0.20 m/s. Air was used as the dispersed phase, and various water-monoethylene glycol solutions were employed as the liquid phase. The water-monoethylene glycol solutions that were tested correspond to a viscosity between 0.9 mPa s and 7.97 mPa s, a density between 997.086 kg/m3 and 1094.801 kg/m3, a surface tension between 0.0715 N/m and 0.0502 N/m, and log10(Mo) between −10.77 and −6.55 (where Mo is the Morton number). Gas holdup measurements were used to investigate the global fluid dynamics and the flow regime transition between the homogeneous flow regime and the transition flow regime. An image analysis method was used to investigate the bubble size distributions and shapes for different gas superficial velocities, for different solutions of water-monoethylene glycol. In addition, based on the experimental data from the image analysis, a correlation between the bubble equivalent diameter and the bubble aspect ratio was proposed. The dual effect of viscosity, previously verified in smaller bubble columns, was confirmed not only with respect to the gas holdup and flow regime transition, but also for the bubble size distributions. Low viscosities stabilize the homogeneous flow regime and increase the gas holdup, and are characterized by a larger number of small bubbles. Conversely, higher viscosities destabilize the homogeneous flow regime and decrease the gas holdup, and the bubble size distribution moves toward large bubbles. The experimental results suggest that the stabilization/destabilization of the homogeneous regime is related to the changes in the bubble size distributions and a simple approach, based on the lift force, was proposed to explain this relationship. Finally, the experimental results were compared to the dual effect of organic compounds and inorganic compounds: future studies should propose a comprehensive theory to explain all the dual effects observed. © 2016 Elsevier Lt

H2 production from bioethanol and its use in fuel-cells

Bioethanol was considered as raw material for hydrogen production by steam reforming, coupled with a proton exchange membrane fuel cell for heat and power cogeneration (5 kWelectrical + 5 kWthermal). The water/ethanol feeding ratio and the ethanol purity were considered for process optimisation. An increase of the water/ethanol ratio improved H2 yield at the expenses of higher heat input to the reformer and lower electrical output. However, the presence of a high enthalpy exhaust stream increased the available thermal output, with a consequent increase of the thermal and overall efficiency of the plant. Finally, the bioethanol purification step, which is energy- and cost-intensive, has been taken into account, searching for an optimisation of the bioethanol purification strategy for the overall process intensification

CO2-mixture properties for pipeline transportation in the CCS process

Transport is an essential feature of the CCS process as the CO2 quality required for transport may influence the choice of the capture technology and impose limits on the performance requirements. Therefore, to design CO2 transport networks, it is important to have an accurate knowledge of the thermodynamic properties of CO2-mixtures. In this paper the results of different EOS (both cubic equations as Peng-Robinson or Redlich-Kwong-Soave and non-analytical equations as Benedict-Webb-Rubin- Starling, Lee-Kesler or GERG model) have been compared with P-ρ-T experimental data obtained by the authors. The Lee-Kesler equation and the GERG model showed a good prediction of CO2-mixture density in the working conditions of the pipeline transport. Finally, simulations of pipelines that transport pure CO2 and CO2-mixtures have been performed and discussed

Cystatin C as a nmarker of renal function Immediately after liver transplantation

To verify whether cystatin C may be of some use as a renal function marker immediately after orthotopic liver transplantation (OLT), we compared serum cystatin C (S(Cyst)), serum creatinine (S(cr)), and creatinine clearance (C(cr)) levels with the glomerular filtration rate (GFR). On postoperative days 1, 3, 5, and 7, S(Cyst) and S(cr) was measured in simultaneously drawn blood samples, whereas C(cr) was calculated using a complete 24-hour urine collection. The GFR was determined on the same days by means of iohexol plasma clearance (I-GFR). The correlation between 1/S(Cyst) and I-GFR was stronger than that of 1/S(cr) or C(cr) (P< 0.01). In the case of moderate reductions in I-GFR (80-60 mL/minute/1.73 m), S(cr) remained within the normal range, whereas the increase in S(cyst) was beyond its upper limit; for I-GFR reductions to lower levels (59-40 mL/minute/1.73 m), S(cr) increased slightly, whereas S(cyst) was twice its upper normal limit. When we isolated all of the I-GFR values on days 3, 5, and 7 that were > or = 30% lower than that recorded on the first postoperative day, S(Cyst)(P< 0.0001) and S(cr) (P< 0.01) levels were increased, whereas C(cr) remained unchanged (P = 0.09). Receiver operating characteristic (ROC) area-under-the-curve analysis showed that the diagnostic accuracy of S(cyst) was better than that of S(cr) and C(cr). S(cyst) levels of 1.4, 1.7, and 2.2 mg/L respectively predicted I-GFR levels of 80, 60, and 40 mL/minute/1.73 m. In conclusion, cystatin C is a reliable marker of renal function during the immediate post-OLT period, especially when the goal is to identify moderate changes in GFR

Practice patterns and 90-day treatment-related morbidity in early-stage cervical cancer

To evaluate the impact of the Laparoscopic Approach to Cervical Cancer (LACC) Trial on patterns of care and surgery-related morbidity in early-stage cervical cancer