Low temperature water vapor pressure swing for the regeneration of adsorbents for CO₂ enrichment in greenhouses via direct air capture

CO2 enrichment in greenhouses can be achieved by extracting CO2 from the outside air. For this purpose, adsorbents based on Na2CO3 or K2CO3 are promising for trapping and releasing atmospheric CO2. Even though the CO2 capture by these adsorbents has been studied before, there is not much information about their regeneration at low temperatures and using air as flushing gas. In this work an experimental design study has been performed to understand the effect of temperature, water vapor pressure and air flow rate on CO2 desorption. The results show that K-based adsorbents are a more attractive option given their higher CO2 capture capacity and lower energy consumption compared to the Na-based ones. The estimated amount of K-based adsorbent with a capture capacity of 0.1 mmol CO2/gads and regenerated at 50 °C with 90 mbar H2O would occupy only 2% of the total volume contained in a closed greenhouse, fulfilling its daily CO2 demand

Pyrolysis oil utilization in 50KWE gas turbine

The concept of using pyrolysis oil (PO) derived from biomass via a fast pyrolysis route for power and heat generation encounters problems due to an incompatibility between properties (physical and chemical) of bio-oil and gas turbines designed for fossil fuels. An extensive research has been performed on the production and improvement of pyrolysis oil but only few investigations were carried out on its utilization. The latter have shown a major difference in behavior of pyrolysis oil compared to fossil fuels during combustion processes. In this work, pyrolysis oil is co-fired with diesel in a 50 kWe gas turbine operating in idle mode. Stable mixtures with up to 20 wt.% of pyrolysis oil and diesel fuel were produced with utilization of a surfactant agent. To prevent feeding line deterioration due to acidic character of pyrolysis oil, a stainless steel nozzle was employed. Furthermore, the fuel emulsion was preheated up to maximum temperature of 80 oC in order to reduce the effect of high viscosity on the atomization process. Diesel distillate #2 was used as a reference fuel for a comparison of gas turbine performance and emissions with various PO content in the blends. During the combustion investigations, the amount of pyrolysis oil was gradually increased with simultaneous decrease of preheating temperature. In all investigated cases, the gas turbine was running stable at its maximum rotational speed (RPM). The CO level resulting from the study with different blends was generally slightly higher in relation to the diesel distillate fuel. NO emissions were in the range of few ppm and almost no detectable with common gas analyzing equipment. After a few hours of continuous operation, there were no signs of deterioration or contaminations inside the combustor. The study shows that pyrolysis oil gradually can be introduced in the market of fossil fuels and benefit to green power generation

Recovery of chemical energy from retentates from cascade membrane filtration of hydrothermal carbonisation effluent

Organic fraction of municipal solid waste is a type of biomass that is attractive due to its marginal cost and suitability for biogas production. The residual product of organic waste digestion is digestate, the high moisture content of which is a problem, even after mechanical dewatering, due to the significant heat requirement for drying. Hydrothermal carbonisation is a process that can potentially offer great benefits by improved mechanical dewatering and valorisation of the digestate into a better-quality solid fuel. However, such valorisation produces liquid by-product effluent rich in organic compounds. Membrane separation could be used to treat such effluent and increase the concentration of the organic compounds while at the same time facilitating the recovery of clean water in the permeate. This work presents the results of the investigation performed using polymeric membranes. The study showed that membrane separation keeps a significant fraction of organics in the retentate. Such concentration significantly increases the biomethane potential of such effluent as well as the energy that could be theoretically used for the generation of process heat using the concentrated retentate in the wet oxidation process.Web of Science284art. no. 12852

Hydrothermal Carbonisation as Treatment for Effective Moisture Removal from Digestate—Mechanical Dewatering, Flashing-Off, and Condensates’ Processing

One of the processes that can serve to valorise low-quality biomass and organic waste is hydrothermal carbonization (HTC). It is a thermochemical process that transpires in the presence of water and uses heat to convert wet feedstocks into hydrochar (the solid product of hydrothermal carbonization). In the present experimental study, an improvement consisting of an increased hydrophobic character of HTC-treated biomass is demonstrated through the presentation of enhanced mechanical dewatering at different pressures due to HTC valorisation. As part of this work’s scope, flashing-off of low-quality steam is additionally explored, allowing for the recovery of the physical enthalpy of hot hydrochar slurry. The flashing-off vapours, apart from steam, contain condensable hydrocarbons. Accordingly, a membrane system that purifies such effluent and the subsequent recovery of chemical energy from the retentate are taken into account. Moreover, the biomethane potential is calculated for the condensates, presenting the possibility for the chemical energy recovery of the condensates.Web of Science1613art. no. 510

Role of dolomite as an in-situ CO2 sorbent and deoxygenation catalyst in fast pyrolysis of beechwood in a bench scale fluidized bed reactor

The dual effect of dolomite as a CO2 sorbent and deoxygenation catalyst in fast pyrolysis of beechwood was investigated. Investigation was performed on a bench scale fluidized bed reactor at an pyrolysis temperature of 500 °C and at different WHSV. CO2 breakthrough curves and bio-oil samples were produced simultaneously. The results show that dolomite is both a feasible catalyst and a CO2 sorbent as it produced a moderately deoxygenated bio-oil and a CO2 free and H2 rich gas. Acids were eliminated, whereas the concentration of methylated phenols and methylated cyclopentanones were enhanced. These results were achieved when rapid carbonation stage was prevailing throughout the experimental run. An organic rich bio-oil with 9.46 wt% yield and a HHV of 28.0 MJ/kg (as received) was obtained. The pH of the catalytic bio-oil increased from 3.2 to 6.0 and the oxygen content reduced to 21.5 wt% from 47.3 wt%. Moreover, the moderately deoxygenated bio-oil is of interest as it can undergo downstream reforming into wide range of liquid fuels with reduced H2 consumption. Calculations show that the H2 generated as a result of CO2 sorption can suffice the requirement for hydrodeoxygenation. In addition the catalysts were also characterized by BET, XRD and SEM analysis

Biomass Fast Pyrolysis Vapor Upgrading over γ-Alumina, Hydrotalcite, Dolomite and Effect of Na2CO3 Loading: A Pyro Probe GCMS Study

The influence of γ-alumina, hydrotalcite, dolomite and Na2CO3 loaded γ-alumina, hydrotalcite, dolomite on fast pyrolysis vapor upgrading of beechwood was investigated using an analytical pyro probe-gas chromatography/mass spectrometry instrument (Py-GC/MS) at a temperature of 500 °C. Overall, this research showcased that these catalysts can deoxygenate biomass pyrolysis vapors into a mixture of intermediate compounds which have substantially lower oxygen content. The intermediate compounds are deemed to be suitable for downstream hydrodeoxygenation processes and it also means that hydrogen consumption will be reduced as a result of moderate in-situ deoxygenation. Among the support catalysts, the application of hydrotalcite yielded the best results with the formation of moderately deoxygenated compounds such as light phenols, mono-oxy ketones, light furans and hydrocarbons with a TIC area % of 7.5, 44.8, 9.8 and 9.8, respectively. In addition, acids were considerably reduced. Dolomite was the next most effective catalyst as γ-alumina retained most of the acids and other oxygenates. Na2CO3 loading on γ-alumina had a noticeable effect on eliminating more or less all the acids, enhancing the mono-oxy-ketones and producing lighter furans. In contrast, Na2CO3 loading on dolomite and hydrotalcite did not show a major impact on the composition except for further enhancing the mono-oxy-ketones (e.g., acetone and cyclopentenones). Additionally, in the case of hydrotalcite and γ-alumina, Na2CO3 loading suppressed the formation of hydrocarbons. In this research, the composition of pyrolytic vapors as a result of catalysis is elaborated further under the specific oxygenate groups such as acids, phenolics, furanics, ketones and acids. Further the catalysts were also characterized by BET, XRD and TGA analysis

CO2 capture from ambient air using hydrated Na2CO3 supported on activated carbon honeycombs with application to CO2 enrichment in greenhouses

CO2 capture from ambient air is an interesting option for CO2 enrichment in greenhouses. In this study, adsorbents comprised of hydrated Na2CO3 supported over activated carbon honeycombs were prepared, characterized and tested for CO2 capture from air. The adsorption of H2O and the formation of the hydrates were studied by means of FT-IR spectroscopy. The inlet CO2 concentration showed to have a major influence on the conversion yield into NaHCO3, and the results fitted well to the Toth model. A statistical model of the CO2 capture capacity was obtained to get insight into the key parameters of the adsorption process. The air temperature and its moisture content showed to have the largest impact on the CO2 capture, while the flow rate had a minor influence. The chemical reaction path during the CO2 adsorption showed to be determined by the relative humidity conditions inside the reactor. Addition of more salt on the carrier showed to improve the CO2 capture capacity, but this is limited by the strength of the honeycomb carrier. Finally, a preliminary desorption test via a mild temperature and moisture swing was run to assess the feasibility of the process for application in greenhouses. The results showed that the required volume of adsorbent would be roughly 1/1000 of the total volume of a closed greenhouse assuming a target CO2 level of 1200 ppm

Numerical modelling of char formation during glucose gasification in supercritical water

Supercritical water gasification is an efficient thermochemical conversion process to convert wet biomass into a high grade fuel. However, char formation during the conversion might influence the process efficiency and operational stability. Providing insight into char formation behavior during the gasification process will facilitate the utilization of this technology. Computational fluid dynamic modelling is used to study the supercritical water gasification of glucose in a tubular helical reactor, which includes an injector tube to mix glucose feed with pre-heated water to provide fast heating. Validation against experimental data confirms that the developed model performs well. An average discrepancy of 4% is obtained for the total feed conversion whereas the gas yield at high temperature is computed with 15% difference. The char yield trend is also captured well. Sensitivity analysis reveals that the presence of low temperature zone at the injection point plays a significant role in char formation

Catalytic Flash Pyrolysis of Biomass Using Different Types of Zeolite and Online Vapor Fractionation

Bio-oil produced from conventional flash pyrolysis has poor quality and requires expensive upgrading before it can be used as a transportation fuel. In this work, a high quality bio-oil has been produced using a novel approach where flash pyrolysis, catalysis and fractionation of pyrolysis vapors using two stage condensation are combined in a single process unit. A bench scale unit of 1 kg/h feedstock capacity is used for catalytic pyrolysis in an entrained down-flow reactor system equipped with two-staged condensation of the pyrolysis vapor. Zeolite-based catalysts are investigated to study the effect of varying acidities of faujasite Y zeolites, zeolite structures (ZSM5), different catalyst to biomass ratios and different catalytic pyrolysis temperatures. Low catalyst/biomass ratios did not show any significant improvements in the bio-oil quality, while high catalyst/biomass ratios showed an effective deoxygenation of the bio-oil. The application of zeolites decreased the organic liquid yield due to the increased production of non-condensables, primarily hydrocarbons. The catalytically produced bio-oil was less viscous and zeolites were effective at cracking heavy molecular weight compounds in the bio-oil. Acidic zeolites, H-Y and H-ZSM5, increased the desirable chemical compounds in the bio-oil such as phenols, furans and hydrocarbon, and reduced the undesired compounds such as acids. On the other hand reducing the acidity of zeolites reduced some of the undesired compounds in the bio-oil such as ketones and aldehydes. The performance of H-Y was superior to that of the rest of zeolites studied: bio-oil of high chemical and calorific value was produced with a high organic liquid yield and low oxygen content. H-ZSM5 was a close competitor to H-Y in performance but with a lower yield of bio-oil. Online fractionation of catalytic pyrolysis vapors was employed by controlling the condenser temperature and proved to be a successful process parameter to tailor the desired bio-oil properties. A high calorific value bio-oil having up to 90% organics was produced using two staged condensation of catalytic pyrolysis vapor. Zeolite-based acidic catalysts can be used for selective deoxygenation, and the catalytic bio-oil quality can be further improved with staged vapor condensatio

An overview of catalysts in biomass pyrolysis for production of biofuels

In-situ catalytic pyrolysis of biomass has been extensively studied in recent years for cost-competitive production of high quality bio-oil. To achieve that, numerous catalysts have been studied to facilitate in-situ upgrading of low-grade condensable vapors (bio-oil) by converting oxygenated compounds and large-molecule species. In this review, these catalysts are categorized in different families and a systematic evaluation of the catalyst effects on pyrolysis products and their characteristics is carried out with respect to the scale of the experimental setup. Among these catalysts, microporous zeolites are considered as most promising in terms of performance and the potential to tailor the desired bio-oil properties. More specifically, the prominent advantages of zeolites include efficient deoxygenation and molecular weight reduction of the resultant bio-oil, while the main drawbacks are decreases in the yield of bio-oil’s organic phase and catalyst deactivation by coke deposition. In addition to the zeolite-based catalysts, other catalysts including mesoporous aluminosilicates, a widely-applied class of catalysts used for deoxygenation of bio-oil as well as alkaline compounds are also reviewed and discussed herein. The research on the latter has not been extensive but the preliminary results have revealed their potential for deoxygenation of bio-oil, production of hydrocarbons, and reduction of undesired compounds. Nevertheless, these catalysts need to be further investigated systematically. Overall, further development of dedicated catalysts for selective deoxygenation and cracking of bio-oil would be essential for scaling up the existing pyrolysis technologies to achieve commercial production of biofuels through pyrolysis