Modelling the performance of a syngas fuelled engine: effect of excess air and CO2 as combustion diluents

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Enhancement of gasification in oxyfuel BECCS cycles employing a direct recycling CO2 utilisation process

No abstract available

Enhancement of gasification in oxyfuel BECCS cycles employing a direct recycling CO2 utilisation process

A new method for improving the efficiency of oxyfuel gasification in biomass energy with carbon capture and storage (BECCS) cycles using carbon dioxide recycled from exhaust gases is described and modelled. Thermodynamic simulations in ASPEN Plus show this process can increase the indicated efficiency of a representative cycle by up to 10.3 % in part by reducing the oxygen requirements for the gasification reaction. Details of syngas production, process cold gas efficiency (CGE), and resulting system temperatures reveal the thermodynamic mechanisms contributing to the observed trends in overall cycle energy efficiency. Exhaust recycling is also shown to have a practical limit beyond which the syngas fuel becomes highly diluted, resulting in low combustion and exhaust temperatures which negatively influence the gasification process. For the system presented here, CO2-enhanced oxy–gasification is thermodynamically limited to oxygen equivalence ratios above λ = 0.13 and equilibrium temperatures above 576 °C. This thermodynamically limited case produced an indicated system efficiency of 26.9 % based on supplied biomass lower heating value (LHV). Further simulations using both ideal cycles and detailed numerical models highlight the influence of several operational settings on the thermodynamic conditions of the gasification process. Principally, the coupling between exhaust temperatures, allothermal heat, and syngas quality are shown to govern the performance of the gasification reactions.ISSN:0196-8904ISSN:1879-222

A novel BECCS power cycle using CO2 exhaust gas recycling to enhance biomass gasification

Although not yet a mature technology, biomass energy with carbon capture and storage (BECCS) is expected to be the leading negative emissions technology deployed over the 21st century to reduce greenhouse gas (GHG) emissions. In this paper, a novel BECCS cycle using exhaust gas recycling (EGR)-enhanced biomass gasification is described and analysed. This cycle combines an atmospheric gasifier and an Otto cycle engine operating under an oxy-gasification/combustion CCS scheme. Exhaust gasses from the Otto cycle, rich in CO2 and at high temperature, are recycled to the gasifier to enhance syngas production. Analysis of a representative numerical model illustrates how EGR creates higher system efficiency and lower specific CO2 emissions while allowing for lower gasifier O2 equivalence ratios (E/R). Compared to a similar power cycle without EGR, the proposed cycle improved system efficiency from 21.7% to 28.8% while reducing specific CO2 emissions from the cycle by 25%

Thermodynamic limitations to direct CO2 utilisation within a small-scale integrated biomass power cycle

Partially recycling CO2-rich exhaust gases from a syngas fuelled internal combustion engine to a biomass gasifier has the capability to realise a new method for direct carbon dioxide utilisation (CDU) within a bioenergy system. Simulation of an integrated, air-blown biomass gasification power cycle was used to study thermodynamic aspects of this emerging CDU technology. Analysis of the system model at varying gasifier air ratios and exhaust recycling ratios revealed the potential for modest system improvements under limited recycling ratios. Compared to a representative base thermodynamic case with overall system efficiency of 28.14 %, employing exhaust gas recycling (EGR) enhanced gasification system efficiency to 29.24 % and reduced the specific emissions by 46.2 gCO2/kWh. Further investigation of the EGR-enhanced gasification system revealed the important coupling between gasification equilibrium temperature and exhaust gas temperature through the syngas lower heating value (LHV). Major limitations to the thermodynamic conditions of EGR-enhanced gasification as a CDU strategy result from the increased dilution of the syngas fuel by N2 and CO2 at high recycling ratios, restricting equilibrium temperatures and reducing gasification efficiency. N2 dilution in the system reduces the efficiency by up to 2.5 % depending on the gasifier air ratio, causing a corresponding increase to specific CO2 emissions. Thermodynamic modelling indicates pre-combustion N2 removal from an EGR-gasification system could decrease specific CO2 emissions by 9.73 %, emitting 118.5 g/kWh less CO2 than the basic system.ISSN:0196-8904ISSN:1879-222

A novel BECCS power cycle using CO2 exhaust gas recycling to enhance biomass gasification

Although not yet a mature technology, biomass energy with carbon capture and storage (BECCS) is expected to be the leading negative emissions technology deployed over the 21st century to reduce greenhouse gas (GHG) emissions. In this paper, a novel BECCS cycle using exhaust gas recycling (EGR)-enhanced biomass gasification is described and analysed. This cycle combines an atmospheric gasifier and an Otto cycle engine operating under an oxy-gasification/combustion CCS scheme. Exhaust gasses from the Otto cycle, rich in CO2 and at high temperature, are recycled to the gasifier to enhance syngas production. Analysis of a representative numerical model illustrates how EGR creates higher system efficiency and lower specific CO2 emissions while allowing for lower gasifier O2 equivalence ratios (E/R). Compared to a similar power cycle without EGR, the proposed cycle improved system efficiency from 21.7% to 28.8% while reducing specific CO2 emissions from the cycle by 25%

Asymmetric Cationic Gemini Surfactants: An Improved Synthetic Procedure and the Micellar and Surface Properties of a Homologous Series in the Presence of Simple Salts

The micellar and morphological properties of symmetric, cationic gemini surfactants have been well studied in the literature as a function of nature and type of the spacer group, and the length and type of hydrophobic chain. In this paper, we have examined the effects of tail asymmetry on the properties of a series of cationic surfactants, the N-alkyl1-N’-alkyl2-N,N,N’,N’-tetramethyldiammonium dibromide. A novel synthetic method is used to prepare a series of these surfactants and the consequences of asymmetry on micellar properties are presented. This new method has been shown to be more efficient, with higher yields of the asymmetric surfactants versus the accepted literature method. The CMC values and the micelle sizes the asymmetric gemini surfactants, 12-4-12, 12-4-10, 12-4-8, and 12-4-6 gemini surfactants were obtained from conductivity and dynamic light scattering. With increasing chain asymmetry, the size of the micelle increased due to the formation of loose micelles. The addition of NaCl and Na2SO4 to the surfactant solutions increased the aggregate size and this effect was more pronounced with increasing salt concentrations. These results are interpreted in terms of the effect these ions have on the “compactness” of the micelle structure.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author