Techno-Economic Comparison of Integration Options for an Oxygen Transport Membrane Unit into a Coal Oxy-Fired Circulating Fluidized Bed Power Plant.

The inclusion of membrane-based oxygen-fired combustion in power plants is considered an emerging technology that could reduce carbon emissions in a more efficient way than cryogenic oxygen-fired processes. In this paper, a techno-economic assessment was developed for a 863 MWel,net power plant to demonstrate whether this CCS technique results in a reduction in efficiency losses and economic demand. Four configurations based on oxygen transport membranes were considered, while the benchmark cases were the air combustion process without CO2 capture and a cryogenic oxygen-fired process. The type of driving force through the membrane (3-end or 4-end), the point of integration into the oxy-fuel combustion process, the heating system, and the pollutant control system were aspects considered in this work. In comparison, the efficiency losses for membrane-based alternatives were lower than those in the cryogenic oxygen-fired process, reaching savings of up to 14% net efficiency. Regarding the specific energy consumption for CO2 capture, the configuration based on the oxygen transport membrane unit with 4-end mode and hot filtration presented 1.01 kWel,net,·h/kgCO2 captured with 100% CO2 recovery, which is an improvement of 11% compared with the cases using cryogenic oxygen. Comparing economic aspects, the specific investment costs for cases based on the oxygen transport membrane unit varied between 2520 and 2942 $/kWel,net·h. This was between 39.6 and 48.2% above the investment for the reference case without carbon capture. However, its hypothetical implantation could suppose a savings of 10.7% in terms of investment cost compared with cryogenic oxygen-based case. In terms of the levelized cost of electricity and the cost of CO2 avoidance, the oxygen transport membrane configurations achieved more favorable results compared with the cryogenic route, reaching savings up to 14 and 38%, respectively. Although oxygen transport membrane units are currently not mature for commercial-scale applications, the results indicated that its application within carbon capture and storage technologies can be strongly competitive.

Estimation of methane production through the anaerobic digestion of greenhouse horticultural waste: A real case study for the Almeria region.

The methane production of greenhouse horticultural waste (GHW) from Almeria (Spain), from where fruits and vegetables are exported to all parts of Europe, was calculated in this work through a combination of experimental and theoretical methods. To this end, eight samples of GHW were collected and characterized in a waste treatment plant. The collection of samples was fairly distributed throughout the year to ensure a representative characterization. The amount of methane produced in a hypothetical anaerobic digestion process was predicted through empirical models fed by experimental data. The experimental characterization revealed that GHW contained an adequate content of volatile matter (65.72% TS), but a high value for total dry matter (53.46%) and lignin content (9.36%), as well as a low moisture content (46.54%) and C/N ratio (17.46). Inhibiting compounds were also observed in the characterization, such a S (0.43%) and Cl (1.41%). The methane production predicted was 0.229 Nm3 CH4/kg volatile matter, which may seem low in comparison to other waste potentially usable for anaerobic digestion. Nonetheless, the co-digestion of GHW with other waste could be an interesting alternative to enhance methane production and solve seasonality issues. Suitable pre-treatment can be also explored to increase the usability of GHW in anaerobic digestion. All in all, this work establishes a theoretical basis for potential solutions to manage the GHW produced in Almeria.

Biogas upgrading to biomethane as a local source of renewable energy to power light marine transport: Profitability analysis for the county of Cornwall.

In this work, the use of biomethane produced from local biogas plants is proposed as renewable fuel for light marine transport. A profitability analysis is performed for three real biogas production plants located in Cornwall (United Kingdom), considering a total of 66 different scenarios where critical parameters such as distance from production point to gas grid, subsidies, etcetera, were evaluated. Even though the idea is promising to decarbonize the marine transport sector, under the current conditions, the approach is not profitable. The results show that profitability depends on the size of the biogas plant. The largest biogas plant studied can be profitable if feed-in tariffs subsidies between 36.6 and 45.7 €/MWh are reached, while for the smallest plant, subsidies should range between 65 and 82.7 €/MWh. The tax to be paid per ton of CO2 emitted by the shipping owner, was also examined given its impact in this green route profitability. Values seven times greater than current taxes are needed to reach profitability, revealing the lack of competitiveness of renewable fuels vs traditional fuels in this application. Subsidies to make up a percentage of the investment are also proposed, revealing that even at 100% of investment subsidized, this green approach is still not profitable. The results highlight the need for further ambitious political actions in the pursuit of sustainable societies.

Characterization of emissions of condensable particulate matter under real operation conditions in cement clinker kilns using complementary experimental techniques.

Historically, the emission of particles from clinker kiln stacks has been one of the main environmental concerns in cement manufacturing processes. Up to now, environmental regulations have only focused on determining and controlling filterable particulate matter (FPM) in industrial emission sources. However, in recent years a growing interest in determining and analysing condensable particulate matter (CPM) has been evidenced due to the significant and established contribution of CPM to total emissions of particulate matter (PM). In this work, total PM (FPM + CPM) emissions from a clinker kiln in a cement manufacturing process have been characterized. A series of tests were performed to simultaneously collect FPM and CPM using a sampling train patented by University of Seville. The results showed very low level of emissions compared to regulatory limits. The average FPM and CPM concentrations obtained in the kiln were in the same order of magnitude, at 3.4 mg/Nm3 and 2.8 mg/Nm3, respectively. The CPM analysed was predominantly inorganic and represented 46% of total PM emissions. In addition, a microscopic morphological analysis was carried out on the samples and confirmed the presence of CPM with a size of less than 2 µm, as well as establishing the principal constituent elements of the same. The main element components were Al, Ca, Fe, Si, C and O. Compounds such as CaCO3, alite, ferrite and dolomite were detected with analytical characterization techniques, such as infrared spectroscopy (FTIR) analysis and X-ray diffraction (XRD), providing a better understanding of the sources of contamination within CPM.