• Energy Research

Abstract The feasibility of reusing waste materials as an inexpensive sorbent to remove volatile organic compounds from gaseous waste streams has been demonstrated. Ashes from wood-chips were tested as sorbent materials for VOCs removal with a PTR-ToF-MS instrument. Both scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) and BET analysis were used to identify the structural characteristics, elemental composition and surface area of the tested ashes respectively. Most of the tentatively identified compounds were less strongly adsorbed by wet ash: thiols, siloxanes, carbonyl compounds and terpenes. Hydrogen sulfide and alcohols show improving removal performance in wet conditions. These results are related to the water solubility properties. Siloxanes were tentatively identified and monitored with PTR-ToF-MS. This demonstrates how this instrument is a suitable tool for simultaneously providing a multitude of analysis for rapid in situ monitoring of fuel contaminants. Considering the low cost, and the recycling of environmental pollutants, wood ashes are a possible choice for VOCs removal from biogas.

Organic Fraction of Municipal Solid Waste was adopted to produce biogas to feed a SOFC generator. Several experimental tests were accomplished on the trace compounds monitoring with PTR-ToF-MS instrument. The main organic compounds detected with the instrument were: sulfurs, terpenes, carboxyls, carbonyls and siloxanes. Coupled to these tests SOFC experiments were accomplished investigating the slipover influence from sorbent materials of sulfurs, chlorines and siloxanes. Limiting factors were evidenced from sulfur, chlorine and siloxane impact on SOFC using an electrochemical impedance spectroscopy (EIS). Tolerable concentration level of single organic compounds appears to be below 1 ppm(v) for H2S and no concentration is tolerated for siloxanes.

The present work investigates electricity production using a high efficiency electrochemical generator that employs as fuel a biogas from the dry anaerobic digestion of the organic fraction of municipal solid waste (OFMSW). The as-produced biogas contains several contaminants (sulfur, halogen, organic silicon and aromatic compounds) that can be harmful for the fuel cell: these were monitored via an innovative mass spectrometry technique that enables for in-line and real-time quantification. A cleaning trap with activated carbons for the removal of sulfur and other VOCs contained in the biogas was also tested and monitored by observing the different breakthrough times of studied contaminants. The electrochemical generator was a commercial Ni anode-supported planar Solid Oxide Fuel Cell (SOFC), tested for more than 300 h with a simulated biogas mixture (CH4 60 vol.%, CO2 40 vol.%), directly fed to the anode electrode. Air was added to promote the direct internal conversion of CH4 to H2 and CO via partial oxidation (POx). The initial breakthrough of H2S from the cleaning section was also simulated and tested by adding ∼1 ppm(v) of sulfur in the anode feed; a full recovery of the fuel cell performance after 24h of sulfur exposure (∼1 ppm(v)) was observed upon its removal, indicating the reliable time of anode exposure to sulfur in case of exhausted guard bed.

Volatile Organic Compounds (VOCs) formed during anaerobic digestion of aerobically pre-treated Organic Fraction of Municipal Solid Waste (OFMSW), have been monitored over a 30 day period by a direct injection mass spectrometric technique: Proton Transfer Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS). Most of the tentatively identified compounds exhibited a double-peaked emission pattern which is probably the combined result from the volatilization or oxidation of the biomass-inherited organic compounds and the microbial degradation of organic substrates. Of the sulfur compounds, hydrogen sulfide had the highest accumulative production. Alkylthiols were the predominant sulfur organic compounds, reaching their maximum levels during the last stage of the process. H(2)S formation seems to be influenced by the metabolic reactions that the sulfur organic compounds undergo, such as a methanogenesis induced mechanism i.e. an amino acid degradation/sulfate reduction. Comparison of different batches indicates that PTR-ToF-MS is a suitable tool providing information for rapid in situ bioprocess monitoring.

Abstract Biogas from the dry anaerobic digestion of OFMSW from a pilot plant was analyzed in terms of sulfur compound removal through a gas cleaning section based on activated carbons, from lab. scale to real plant. In general, even the presence of sub-ppm(v) of selected biogas contaminants can hamper the life-time of SOFC systems. For this reason, stringent fuel cell quality requirements apply. The challenge of real-time monitoring of the performance and quality of the fuel feeding the SOFC can be solved through the use of PTR-MS. This technique – once properly and preliminary calibrated as shown in this study – has the capability of rapidly resolving the wide spectrum of contaminants slipping from the clean-up section. A commercial sorbent material was adopted to remove sulfur compounds and was tested for 80 h in a pilot gas cleaning system. H2S, the main sulfur compound detected (99.36% of total sulfurs) was removed to a satisfactory level. The sulfur compounds elute from the cleaning section in the following order: CH3SH, CH3SCH3, CH3CH2CH2SH, CH3(CH2)3SH, CS2 and H2S. The filter section was able to provide a clean biogas (1 ppm(v)) throughout the whole experimental trial (almost 450 h) with an average H2S inlet concentration of 52 ppm(v).

Vineyard pruning residues are a potential resource of biomass for energy. Nevertheless the possible presence of agrochemicals in this fuel could entail negative environmental consequences during its combustion. In order to verify its sustainability for energy production, a case study was conducted: biomass from common and organic vineyards in Trento Province (Northern Italy) was collected, analyzed, and burned as comminuted fuel in a 180 MJ domestic boiler equipped with a micro electrostatic filter; wood chips and pellets produced with similar raw material (vineyard residues and spruce wood) were used as reference. Flue gases composition was monitored with particular attention to heavy metal contamination. The results, to be considered as preliminary, show that vineyard residues had higher emissions compared to the remaining fuels, including organic vineyard residues, but always within the limits prescribed in Italy. In terms of total heavy metal emissions no significant differences could be detected among the tested fuels. The electrostatic filter proved to be effective in the reduction of total fly ash emissions as well as the use of pelletized biomass. © 2013 Elsevier Ltd. All rights reserved.

A practical and feasible solution to reduce the global impacts from fossil fuels is represented by the locally distributed micro-cogeneration systems with high temperature solid oxide fuel cells (SOFC) fed by biogenous fuel coupled in an energy distributed system. One of the main drawback is the low tolerability towards certain fuel impurities, mostly sulfur, chlorine and siloxane compounds. The opportunity to predict the breakthrough time of a gas cleaning section with a high precision level is mandatory to meet SOFC requirements. The reaction kinetic equation called the Wheeler-Jonas equation is adopted to estimate this breakthrough time. Two different commercial activated carbons were studied estimating the breakthrough time varying the operating temperature, the pollutant concentration (single and multiple effects) and the relative humidity. Results showed how relative humidity content affects inversely the removal performance for both sorbents. The Carbox sample, below RH 20% showed interesting results due to its metals content and microstructure. Here, relative humidity promoted the best condition to remove organic vapors from the biogas stream. Multiple contaminant conditions for both sorbent materials decreased the removal performance (tb). This decreasing for the Carbox sample ranged from a minimum of 44% to a maximum of 50% for H2S, and 70% for HCl with wet and dry conditions respectively.

The technique of proton transfer reaction mass spectrometry (PTR-MS) couples a proton transfer reagent, usually H3O+, with a drift tube and mass spectrometer to determine concentrations of volatile organic compounds. Proton transfer reaction-mass spectrometry (PTR-MS) has successfully been applied to a wide variety of matrices to identify and to investigate on the behavior of trace compounds; among the possible field of applications we can find: food, air, energy, etc. Natural gas is considered as a fuel for high energy efficiencies applications such as SOFC generators. The ability to distinguish several isobaric aldehydes, ketones, isoprenoids and other compounds is impossible using PTR-MS instrument. In the present research work, PTR-ToF-MS was coupled to a prototype FastGC system allowing for a rapid (90 s) chromatographic separation of the sample headspace prior to PTR-MS analysis. The system was tested on natural gas trace compounds to individuate the major elements and to identify possible issues for the SOFC generators. In comparison to the results obtained by direct injection, FastGC provided additional information, thanks to a less drastic dilution of the sample and due to the chromatographic separation of isomers. This was achieved without increasing duration and complexity of the analysis.

Microalgae present promising green economy applications in the energy and biorefinery sectors. The work concerns a pilot study on the integration of anaerobic digestion with microalgae cultivation for managing at the same time emissions and digestate from the dry anaerobic treatment of organic waste. Biogas produced was used to feed Solid Oxide Fuel Cell after a filtering step for removing toxic compounds. The exhausts and digestate were used for providing carbon and nutrients for microalgae growth. The experimental workflow includes the characterization of both for defining their suitability in the microalgal growth (Chlorella vulgaris) tests. The exhausts of Solid Oxide Fuel Cells showed relatively stable concentration of CH4 (4–7%) and CO2 (93–96%) and low concentrations (sub ppm(v)) of sulphur, carbonyl and carboxyl, and aromatic compounds and terpenes, making it particularly suited for algae growing as compared with internal combustion engines. The challenging growing conditions are a compromise between carbon recovery and use of digestate. A good microalgae growth has been obtained (22.31 mm3 mL−1 of biovolume corresponding to 151 dry mg L−1 day−1) exploiting ammonia and phosphate from dilute digestate (removal efficiency 94% and 30% respectively) as well as a good carbon recovering (310 mg CO2 L−1 day−1). Based on our data, the integration of microalgae growth and anaerobic digestion process seems a viable solution to achieve (i) reduced emissions due to carbon recovery; (ii) optimum integrated management of anaerobic digestion waste and (iii) biomass production by low-cost nutrients and carbon.

Abstract The research efforts for SOFC plants fed by biogas moved from the prototypal research to the feasibility of pilot plants up to achieve industrial size plants. Siloxanes among the other trace compounds contained in biogas appear to be the most detrimental for the fuel cell performance. Siloxanes are difficult to be detected and monitored continuously in the gas matrix. A direct injection mass spectrometry technique (PTRMS) was adopted for the monitoring of siloxane removal. Commercial and waste derived sorbent materials are experimentally tested for the removal of siloxanes. Waste derived material was selected to implement the circular recovery purposes. A simple parametric investigation study was developed. It was considered the influence of gas velocity and sulphur compounds, as co-vapors. Physical and chemical characteristics were correlated to the adsorption capacity. Results show three separated groups. Group I shows the best performance in terms of siloxane removal. There is a direct and strong relation between active surface area and microporous volume with the adsorption capacity. This direct correlation is not verified for some elements such as Fe and S, while it is respected for Cu and K. Higher performance are registered for not all the commercial carbons. In fact, the physical structure and impregnating agents are crucial for the siloxane removal.